GIFT   OF 

MICHAEL  REESE 


AMERICAN  SCIENCE  SERIES,  BRIEFER  COURSE 


AN  INTRODUCTION  TO  TflE  STUDY 


OF 


CHEMISTRY 


BY 

IRA   REMSEN 

Professor  of  Chemistry  in  the  Johns  Hopkins  University 


SIXTH  EDITION,  REVISED   AND   ENLARGED 


NEW  YORK 

HENRY  HOLT   AND   COMPANY 
1901 


I  cl  C    1 


Copyright,  1886,  1893,  1901, 

BY 
HENRY  HOLT  &  CO. 


ROBERT   DROMMOND,    PRINTER,    NEW  YORK. 


PEEFACE  TO  THE  SIXTH  EDITION. 

SINCE  the  appearance  of  the  last  edition  of  this  book 
many  important  discoveries  have  been  made  in  Chemistry. 
In  preparing  the  new  edition  the  author  has  endeavored  to 
include  all  discoveries  that  come  within  the  scope  of  the 
book,  and  it  is  believed  that  nothing  that  could  fairly  be 
looked  for  in  a  book  of  this  size  has  been  omitted.  The 
experiments  have  not  been  essentially  changed.  The 
question  whether  it  was  advisable  to  introduce  a  larger 
number  of  quantitative  experiments  was  fully  considered. 
The  conclusion  reached  was  that,  in  the  time  generally 
available,  it  would  be  impossible  properly  to  perform  a 
larger  number  of  such  experiments  than  is  described  in  the 
earlier  editions.  That  has  been  our  experience  in  our  first 
year's  course,  and  it  has  been  the  experience  of  many 
teachers  who  have  kindly  given  the  author  the  benefit  of 
their  advice. 

Some  account  of  the  new  theory  of  solutions  is  given, 
and  its  application  to  the  explanation  of  reactions  that 
take  place  in  water  solutions  receives  consideration.  It 
would,  of  course,  be  an  easy  matter  to  go  further  into  this 
subject,  but  it  does  not  seem  to  the  author  wise  to  do  so 
in  the  earliest  stages  of  the  study  of  Chemistry. 

I.  K. 

BALTIMORE,  May,  1901. 

iii 


221709 


PREFACE  TO  THE   FIRST  EDITION. 

IN  preparing  this  book,  I  have  endeavored  to  keep  in 
mind  the  fact  that  it  is  intended  for  those  who  are  begin- 
ning the  study  of  chemistry.  Instead  of  presenting  a  large 
number  of  facts  and  thus  overburdening  the  student's 
mind,  I  have  presented  a  smaller  number  than  is  usual  in 
elementary  courses  in  chemistry;  but  I  have  been  careful 
to  select  for  treatment  such  substances  and  such  phenomena 
as  seem  to  me  best  suited  to  give  an  insight  into  the  nature 
of  chemical  action.  Usually  the  mind  is  not  allowed  to 
dwell  for  any  length  of  time  upon  any  one  thing  and  thus 
to  become  really  acquainted  with  it,  but  is  hurried  on  and 
is  soon  bewildered  in  the  effort  to  comprehend  what  is 
presented.  I  cannot  but  believe  that  it  is  much  better  to 
dwell  longer  on  a  few  subjects,  provided  these  subjects  are 
properly  selected. 

The  charge  is  frequently  made  that  our  elementary  text- 
books on  chemistry  are  not  scientific;  that  is  to  say,  that 
not  enough  stress  is  laid  upon  the  relations  which  exist 
between  the  phenomena  considered, — the  treatment  is  not 
systematic.  The  student  is  taught  a  little  about  oxygen, 
a  little  about  hydrogen,  a  little  about  nitrogen,  etc. ;  and 
then  a  little  about  potassium,  a  little  about  calcium,  etc. ; 
and  he  is  left  simply  to  wonder  whether  there  is  any  con- 
nection between  the  numerous  facts  offered  for  study.  It 
must  be  acknowledged  that  there  are  serious  difficulties  in 
the  way  of  a  purely  scientific  treatment  of  chemistry,  but 


vi  PREFACE    TO    THE  FIRST  EDITION. 

I  think  that  it  is  quite  possible  to  treat  the  subject  more 
scientifically  than  is  customary,  and  thus  to  make  it  easier 
of  comprehension  to  the  student.  I  have  made  an  effort 
in  this  direction  in  the  book  here  offered  to  the  public. 

In  teaching  chemistry,  two  mistakes  are  commonly 
made.  The  first  is  that  of  presenting  the  profoundest 
theories  of  the  science  before  the  student  is  prepared  for 
them.  Hence  they  make  little  impression  upon  his  mind, 
and  he  only  learns  to  repeat  words  about  them,  without 
having  any  real  comprehension  of  them. 

The  other  mistake  is  that  of  giving  directions  for  experi- 
ments without  making  it  clear  to  the  student  why  they  are 
performed  or  what  they  teach.  The  result  is  that  he  sees 
little  or  no  connection  between  the  subjects  treated  in  the 
text-book  and  the  things  which  he  works  with  in  the 
laboratory. 

Now,  the  first  object  of  a  course  in  science  should  be  to 
develop  a  scientific  habit  of  thought.  This  cannot  be  done 
by  mere  study  of  the  theories  of  a  science,  nor  by  hap- 
hazard experimenting.  It  can  only  be  reached  by  sys- 
tematic study  of  the  phenomena,  and  by  recognizing  the 
connection  between  these  phenomena  and  the  theories. 
At  the  outset  the  best  plan  is  to  study  phenomena  scien- 
tifically, and  afterwards  speculations  may  be  introduced  to 
some  extent;  though,  in  my  opinion,  it  is  better  to  keep 
these  decidedly  subordinate  in  an  elementary  course. 

At  this  day  it  is  almost  superfluous  to  emphasize  the 
great  importance  of  laboratory  work  as  a  part  of  a  course 
in  chemistry.  College  authorities  and  school  boards  are 
beginning  to  recognize  the  necessity  of  this  kind  of  work 
for  the  purpose  of  securing  satisfactory  results.  A  labora- 
tory can  be  fitted  up  at  slight  cost  in  which  all  the  experi- 
ments described  in  this  book  could  be  performed.  It  is 
not  necessary  to  wait  until  a  complete  laboratory  is  pro- 
vided. The  accommodations  needed  are  simple,  and  there 


PREFACE    TO   THE  FIRST  EDITION.  vii 

can  hardly  be  a  college  or  school  which  could  not  with  a 
little  effort  secure  the  few  conveniences.  Should  there, 
however,  be  such  a  place,  the  teacher  can  at  least  perform 
the  experiments  described.  And  this  he  had  better  do 
with  not  more  than  ten  or  a,  dozen  students  around  him. 
By  constantly  questioning  them,  and  getting  one  or 
another  to  help  him,  or  to  do  the  work,  fairly  satisfactory 
results  can  be  attained. 

If  the  students  work  in  the  laboratory,  it  is  of  prime 
importance  that  they  should  not  be  left  to  shift  for  them- 
selves. They  will  surely  acquire  bad  habits  of  work,  and 
will  generally  fail  to  understand  what  they  are  doing.  A 
thorough  system  of  questioning  and  cross-questioning  is 
necessary  in  order  that  the  work  shall  be  successful.  A 
badly-constructed  piece  of  apparatus  should  not  be  allowed, 
and  cleanliness  should  be  insisted  upon  from  the  begin- 
ning. The  instructor  should  be  as  watchful  in  the  labora- 
tory as  in  the  recitation- room,  and  should  be  as  exacting 
in  regard  to  the  experimental  work  as  the  teacher  of 
languages  is  in  regard  to  the  words  of  a  lesson.  A  badly- 
performed  experiment  should  be  considered  as  objection- 
able as  a  bad  recitation  or  a  badly-written  exercise.  When 
teachers  of  chemistry  acquire  this  feeling  and  work  in  this 
spirit,  the  educational  value  of  laboratory  courses  will  be 
greater  than  it  frequently  is  now.  The  average  playing 
with  test-tubes  and  precipitates  is  of  questionable  benefit. 
As  it  has  been  dignified  by  the  undeserved  name  of  scien- 
tific training,  and  put  forward  in  place  of  the  real  thing, 
many  thinking  men  have  been  led  to  question  the  value  of 
scientific  training,  and  to  adhere  to  the  old  drill  in  gram- 
matical forms  and  mathematical  problems.  I  do  not 
wonder  at  this,  but  I  should  be  greatly  surprised  to  find 
this  state  of  mind  continuing  after  really  good  laboratory 
courses  are  provided.  A  slovenly  laboratory  course  in 
chemistry  is  a  poor  substitute  for  a  well-conducted  course 


vni  PREFACE    TO    THE  FIRST  EDITION. 

in  mathematics  or  languages.  It  behooves  those  who  are 
convinced  of  the  great  advantages  to  be  derived  from  good 
laboratory  courses  to  see  to  it  that  these  courses  are  con- 
scientiously conducted. 

A  few  of  the  experiments  described  in  the  book  cannot 
well  be  made  by  every  student  in  the  laboratory.  These 
the  teacher  should  make  at  all  events,  and  he  should  not 
only  make  them,  but  see  to  it  that  every  detail  is 
thoroughly  comprehended  by  the  student.  In  the  direc- 
tions for  the  experiments  the  quantities  recommended  are 
in  some  cases  larger  than  would  be  desirable  for  each 
student.  The  proportions  being  correctly  given  in  the 
book,  the  absolute  quantities  can  be  regulated  by  the 
teacher  to  suit  the  circumstances. 

Finally,  I  invite  correspondence  from  teachers  who  may 
use  the  book,  and  who  may  experience  any  difficulty  in  its 
use.  I  shall  gladly  avail  myself  of  any  suggestion  which 
may  help  towards  making  it  more  useful. 

The  apparatus  needed  can  be  obtained  from  any  dealer 
in  chemical  wares,  and  I  have  no  doubt  that  some  of  the 
larger  houses  would  furnish  estimates  for  all  that  is  neces- 
sary for  the  purpose  of  illustrating  the  course. 

I.  K. 

BALTIMORE,  December  21,  1885. 


PREFACE  TO  THE  THIRD  EDITION. 

THIS  book  has  been  thoroughly  revised  by  me  after  seven 
years'  experience  with  it  in  the  laboratory  and  the  class- 
room, and  I  believe  that  it  will  be  found  to  be  materially 
improved.  In  the  work  of  revision  I  have  been  nrnch  aided 
by  friends  at  home  and  abroad  who  have  made  valuable 
suggestions,  all  of  which  I  have  endeavored  to  consider 
without  prejudice.  Special  attention  has  been  given  to 
the  descriptions  of  the  experiments,  with  the  object  of 
making  them  as  clear  and  as  suggestive  as  possible.  A  few 
which  have  been  found  to  work  unsatisfactorily  have  been 
omitted,  and  a  few  new  ones  have  been  added,  among  the 
latter  being  some  of  a  quantitative  character  which  have 
proved  instructive  where  they  have  been  tried,  and  it  is 
hoped  that,  wherever  the  time  will  permit,  they  may  be 
included  in  the  regular  course. 

The  principal  changes  made  in  the  book  besides  those 
mentioned  are: 

1.  A  somewhat  earlier  introduction  of  the  chapter  on 
the  atomic  theory. 

2.  The   presentation    of   the   periodic   law   before   the 
systematic   study  of  the  elements   is  taken  up,   and  the 
classification  of  the  elements  in  accordance  with  this  law. 

3.  The  addition  of  two  chapters  on  some  of  the  more 
common  compounds  of  carbon. 

4.  The  addition  of  a  chapter  on  qualitative  analysis. 

5.  A  fuller  treatment  of  the  metallic  elements. 


x  PREFACE    TO    THE  SIXTH  EDITION. 

6.  The  use  of  different  type  for  the  experiments  and  for 
the  text;  and  clearer  paragraphing. 

I  take  pleasure  in  thanking  my  assistant,  Dr.  AY.  W. 
RANDALL,  who  has  contributed  to  the  value  of  the  book 
by  helping  me  in  reading  the  proofs  and  by  preparing  the 
index. 

I.  R. 
BALTIMORE,  June,  1893. 


CONTENTS. 


CHAPTER  I. 

CHEMICAL    ACTION ELEMENTS — COMPOUNDS — HOW    TO    STUDY 

CHEMISTRY. 

PAGE 

Introductory — Chemical  changes — Physical  changes — Physics 
and  chemistry — Relations  between  the  different  kinds  of 
change — Chemical  changes  caused  by  heat — Electric  currents 
connected  with  chemical  changes — Chemical  changes  con- 
nected with  the  passage  of  the  electric  current — Electroly- 
sis— Relation  between  chemistry  and  physics — Object  of  the 
chemist's  study — Mechanical  mixtures — One  of  the  chief 
characteristics  of  chemical  action — The  cause  of  chemical 
action — Summary — How  to  study  chemistry — The  elements 
and  their  symbols 1 

CHAPTER  II. 

A  STUDY  OF  THE   ELEMENT  OXYGEN. 

Occurrence  of  oxygen — Preparation  of  oxygen — Preparation  of 
oxygen  from  potassium  chlorate — Oxygen  from  manganese 
dioxide — Oxygen  from  potassium  chlorate  and  manganese  di- 
oxide— Physical  properties  of  oxygen — Chemical  conduct  of 
oxygen — Action  of  oxygen  at  higher  temperatures — Proof 
that  oxygen  combines  with  the  burning  substance — Propor- 
tions by  weight  in  which  the  substances  combine  with  oxy- 
gen— Relation  of  the  weight  of  the  product  to  the  weights  of 
the  combining  substances — Burning  in  the  air — Combustion 
— Kindling-temperature — Slow  oxidation — Breathing — Heat 
of  combustion — How  the  quantity  of  heat  is  measured — Heat 
of  decomposition — Chemical  energy  and  chemical  work  • 

Oxides 21 

xi 


xii  CONTENTS. 

CHAPTER  III. 

HYDROGEN. 

PAO1 

Occurrence — Preparation  of  hydrogen — Action  of  sodium  and 
of  potassium  on  water — Decomposition  of  water  by  iron — 
Decomposition  of  water  by  carbon  or  charcoal — Action  of 
acids  upon  metals — Physical  properties-  of  hydrogen — Chem- 
ical properties  of  hydrogen — Product  formed  when  hydrogen 
burns  in  oxygen 39 

CHAPTER  IV. 

COMBINATION   OF   HYDROGEN  AND   OXYGEN — WATER. 

Occurrence — Water  of  crystallization — Efflorescence — Deliques- 
cence— Analysis  and  synthesis — Decomposition  of  water  by 
the  electric  current  and  what  it  teaches — Synthesis  of  water 
by  burning  hydrogen — Synthesis  of  water  by  mixing  hydro- 
gen and  oxygen — Quantitative  synthesis  of  water — Law  of 
Dalton  and  Gay  Lussac — Correction  for  temperature — Boyle's 
law — Correction  for  pressure — Combined  volumetric  correc- 
tions^— Correction  for  aqueous  pressure — Apparatus  for  meas- 
uring the  volume  of  a  gas — Calculation  of  the  results  ob- 
tained on  exploding  mixtures  of  hydrogen  and  oxygen — 
Synthesis  of  water  by  passing  hydrogen  over  heated  oxides — 
Quantitative  synthesis  of  water — Oxidation  and  reduction — 
The  oxyhydrogen  blowpipe — The  lime-light — Natural  waters 
—Testing  of  drinking-water — Distillation  of  water — Proper- 
ties of  water — Water  as  a  solvent — Solutions  and  chemical 
compounds — Solution  as  an  aid  to  chemical  action — Ozone — 
Hydrogen  dioxide — Summary — Comparison  of  hydrogen  and 
oxygen 49 

CHAPTER  V. 

LAWS     OF     CHEMICAL     COMBINATION — COMBINING     WEIGHTS — 
ATOMIC   WEIGHTS — CHEMICAL  EQUATIONS. 

Law  of  the  indestructibility  of  matter — Law'  of  the  conserva- 
tion of  energy — Law  of  definite  proportions — Law  of  multi- 
ple proportions — Combining  weights  of  elements — Hypothe- 
sis and  theory — The  atomic  theory — Atomic  weights — Inter- 


CONTENTS. 


national  atomic  weights — How  the  relative  weights  of  atoms 
are  determined — Formulas  of  chemical  compounds — Mole- 
cules. . 74 


CHAPTER  VI. 

STUDY  OF  THE  REACTIONS  EMPLOYED  IN  THE  PREPARATION 
OF  OXYGEN  AND  OF  HYDROGEN,  AND  IN  THE  STUDY 
OF  WATER. 

Preparation  of  oxygen — Heating  mercuric  oxide — Quantita- 
tive study  of  the  decomposition  of  potassium  chlorate  by 
heat — Heating  manganese  dioxide — The  action  of  oxygen 
on  carbon,  sulphur,  phosphorus,  and  iron — Preparation  of 
hydrogen — Decomposition  of  water  by  an  electric  current — 
Action  of  sodium  and  01  potassium  on  water — Substitution — 
Action  of  iron  on  water — Decomposition  of  water  by  carbon 
— Action  of  metals  on  acids — Quantitative  study  of  the  ac- 
tion of  acids  on  metals — Action  of  hydrogen  on  copper  oxide 
— Preparation  of  hydrogen  dioxide — Double  decomposition — 
Kinds  of  chemical  reactions — Conditions  under  which  chem- 
ical reactions  take  place 88 


CHAPTER  VII. 

CHLORINE  AND  ITS  COMPOUNDS  WITH  HYDROGEN  AND  OXYGEN. 

Occurrence  —  Preparation  —  Deacon's  process  —  Lab  oratory  • 
Method— Properties  of  chlorine — Action  of  chlorine — Bleach- 
ing by  chlorine — Chlorine  hydrate — Hydrogen  burns  in 
chlorine — Chlorides — Nomenclature  of  chlorides  and  of  ox- 
ides— Hydrochloric  acid — Relation  of  light  to  chemical  ac- 
tion— Preparation  of  hydrochloric  acid — Properties — Com- 
mercial hydrochloric  acid — Pure  hydrochloric  acid — Analysis 
of  hydrochloric  acid — Action  of  liquid  hydrochloric  acid — 
Compounds  of  chlorine  with  oxygen  and  with  hydrogen  and 
oxygen — Compounds  of  chlorine  with  hydrogen  and  oxy- 
gen— Decomposition  of  bleach  ing-powder  by  acids — Other 
compounds  of  chlorine,  hydrogen,  and  oxygen — Compounds 
of  chlorine  and  oxygen 101 


xiv  CONTENTS. 

CHAPTER  VIII. 

ACIDS — BASES — NEUTRALIZATION — SALTS. 

PAGE 

Neutralization — Litmus  test  for  acids  and  alkalies — Quantita- 
tive study  of  neutralization — Ratio  of  acid  to  alkali  in  neu- 
tralization— What  is  formed  when  acid  and  base  are  neutral- 
ized— Importance  of  water  in  the  experiments  on  neutraliza- 
tion— What  is  solution? — Jons  not  the  same  as  atoms — 
Definition  of  acids  and  bases  in  terms  of  the  theory  of  elec- 
trolytic dissociation — Products  of  neutralization — Salts — 
Metallic  elements — Nomenclature  of  acids — Nomenclature  of 
bases — Nomenclature  of  salts — Acid  properties  and  oxygen.  .  121 

CHAPTER  IX. 

NITROGEN — AIR. 

Two  gases  in  the  air — Quantitative  study  of  the  composition  of 
the  air — Nitrogen — Preparation — The  air — Occurr3nce  of 
nitrogen — Properties  of  nitrogen — Other  constituents  of  the 
air — Quantity  of  water-vapor  in  the  air — Quantity  of  carbon 
dioxide  in  the  air — Argon — Liquid  air — Oxygen  prepared 
from  liquid  air — Other  gases  in  the  air 133 

CHAPTER  X. 

COMPOUNDS  OF  NITROGEN  WITH  HYDROGEN  AND  OXYGEN. 

General  conditions  which  give  rise  to  the  formation  of  the 
simpler  compounds  of  nitrogen — Ammonia — Preparation  of 
ammonia — Properties  of  ammonia — Salts  formed  by  ammonia 
— Ammonium  theory — Composition  of  ammonia  by  weight — 
Composition  of  ammonia  by  volume — Relations  between  the 
volumes  of  combining  gases— Gay  Lussac's  law  of  volumes — 
Condensation  or  contraction — Relations  between  the  specific 
gravities  of  gases  and  their  atomic  weights — Nitric  acid — 
Preparation  of  nitric  acid — Nitric  acid  an  oxidizing  agent — 
Action  of  nitric  acid  on  metals — Ammonia  formed  by  reduc- 
tion of  nitric  acid — Aqua  regia — Nitrous  acid — Nitrons  acid 
breaks  down  into  nitrogen  trioxide  and  water — Anhydrides 
— The  oxides  of  nitrogen — Nitrous  oxide — Nitric  oxide — 
Nitrogen  peroxide — Uses  of  the  oxides  of  nitrogen  in  the 
manufacture  of  sulphuric  acid — Summary 143 


CONTENTS.  XV 

CHAPTER  XI. 

CARBON. 

PAGE 

Carbon  in  plants  and  animals — Occurrence — Diamond — Graph- 
ite— Amorphous  carbon — Charcoal — A  charcoal-kiln — Wood- 
charcoal — Coke — Lamp-black — Bone-black,  or  animal  char- 
coal— Charcoal  filters— Wood  is  charred  to  preserve  it — Coal 
— Diamond,  graphite,  and  charcoal  different  forms  •  of  the 
element  carbon — Other  examples  of  the  occurrence  of  a  sub- 
stance in  different  forms — Common  properties  of  the  three 
forms  of  carbon — Chemical  conduct  of  carbon — Direct  union 
of  carbon  and  oxygen — Abstraction  of  oxygen  from  com- 
pounds by  means  of  carbon — Reduction 167 

CHAPTER  XII. 

V 

SOME    OF    THE    SIMPLER    COMPOUNDS    OF    CARBON. 

Compounds  of  carbon  with  hydrogen — Carbon  dioxide — Carbon 
dioxide  given  off  from  the  lungs — Carbon  dioxide  formed  in 
combustion,  in  decay,  and  in  fermentation — Decomposition  of 
carbonates  by  acids — Comparison  of  this  decomposition  with 
other  similar  acts — Preparation  of  carbon  dioxide — Physical 
properties  of  carbon  dioxide — Chemical  properties  of  carbon 
dioxide — Respiration — The  cycle  of  carbon  in  nature — Plants 
and  animals  as  storehouses  of  energy — Carbonic  acid  and  car- 
bonates— Solution  of  calcium  carbonate  in  water  containing 
carbon  dioxide — Carbon  monoxide — Preparation  of  carbon 
monoxide — Illumination,  flame,  blowpipe,  etc. — Illuminating- 
gas — Flames — Kindling-temperature  of  gases — Safety-lamp 
— Structure  of  flames — Blowpipe — Use  of  blowpipe  in  analy- 
sis— Causes  of  the  luminosity  of  flames — Bunsen  burner — 
Cyanogen — Hydrocyanic  acid,  prussic  acid — Carbides — Sum- 
mary   179 


AVOGADRO'S  HYPOTHESIS — MOLECULAR  WEIGHTS — MOLECULAR 
FORMULAS — VALENCE. 

' 


CHAPTER  XIII. 


Avogadro's   hypothesis — Molecules   of   the   elements — Nascent 
state — Relation    of   physios    and    chemistry   to    molecules — 


xvi  CONTENTS. 

PAGE 

Explanation  of  the  laws  governing  the  combination  of  gases 
— How  a  formula  is  determined — Raoult's  laws— Apparent 
exceptions — Determination  cf  molecular  weights  by  the  boil- 
ing-point and  the  freezing-point  methods — Valence — Sub- 
stituting power  of  elements — Variations  in  valence — Sum- 
mary   205 

CHAPTER  XIV. 

CLASSIFICATION    OF    THE    ELEMENTS — PERIODIC    LAW. 

General — Acid  and  basic  properties — Natural  families  of  the 
elements — Relations  between  atomic  weights  of  the  elements 
and  their  properties — The  periodic  law — Composition  of  com- 
pounds with  hydrogen  and  with  oxygen — Acid-forming  and 
base-forming  elements— The  weight  of  its  atom  determines 
the  properties  of  an  element — Plan  to  be  followed 220 

CHAPTER  XV. 

THE  CHLORINE  GROUP: 
CHLORINE,  BROMINE,  IODINE,  FLUORINE. 

Bromine — Preparation — Properties — Hydrobromic  acid — Com- 
pounds with  hydrogen  and  oxygen — Iodine — Properties — 
Hydriodic  acid — iodic  acid— Fluorine — Properties — Hydroflu- 
oric acid — Comparison  of  the  members  of  the  chlorine  group.  220 

CHAPTER  XVI. 

THE  SULPHUR  GROUP: 
SULPHUR,  SELENIUM,  TELLURIUM. 

Sulphur — Extraction  of  sulphur  from  its  ores— Refining  of  sul- 
phur— Properties — Crystals  of  sulphur — Crystallography — 
Chemical  conduct  of  sulphur — Hydrogen  sulphide,  sulphu- 
retted hydrogen — Preparation — Properties — Chemical  analy- 
sis— Hydrosulphides — Compounds  of  sulphur  with  oxygen 
and  with  hydrogen  and  oxygen — Sulphur  dioxide — Sulphur- 
ous acid — Sulphur  trioxide — Sulphuric  acid — Manufacture 
of  sulphuric  acid — Properties  of  sulphuric  aeid — Uses  of  sul- 
phuric acid — Monobasic  and  dibasic  aoids — Acid,  neutral,  and 


CONTENTS.  xvii 

PAGE 

normal  salts — Other  acids  containing  sulphur — Carbon  bisul- 
phide —  Selenium  and  tellurium  and  their  compounds  — 
Points  of  resemblance  between  oxygen  and  the  members  of 
the  suipliur  group 238 

CHAPTER  XVII. 

THE    NITROGEN    GROUP: 
NITROGEN,   PHOSPHORUS,   ARSENIC,   ANTIMONY,   AND    BISMUTH. 

General — Phosphorus — Preparation — Properties — Red  phospho- 
rus— Applications  of  phosphorus — Phosphine,  phosphuretted 
hydrogen — Phosphine  itself  does  not  take  fire  spontaneously 
— Compounds  of  phosphorus  with  oxygen  and  with  hydrogen 
and  oxygen — Orthophosphoric  or  ordinary  phosphoric  acid — 
Metaphosphoric  acid — Phosphorous  acid — Arsenic — Arsine, 
arseniuretted  hydrogen — Properties  of  arsine — Arsenic  tri- 
oxide — Acids  of  arsenic — Antimony — Stibine,  antimoniu- 
retted  hydrogen — Acids  of  antimony — Antimony  as  a  base- 
forming  element — Bismuth — Salts  of  bismuth — Bismuth  ni- 
trates— General  remarks  on  the  characteristics  of  the  nitro- 
gen group — Boron — Boric  acid — Boric  anhydride 258 


CHAPTER  XVIII. 

THE  CARBON  GROUP:     CARBON  AND  SILICON. 
TITANIUM,  ZIRCONIUM,   CERIUM,    THORIUM. 

Silicon — Silicides — Silicic  acid — Silicon  dioxide,  silicic  anhy- 
dride— Comparison  of  carbon  and  silicon — Rare  elements  of 
this  group 274 

CHAPTER  XIX. 

BASE-FORMING  ELEMENTS — GENERAL  CONSIDERATIONS. 

Introductory — Order  in  which  the  base-forming  elements  will 
be  taken  up — Metallic  properties — Occurrence  of  the  metals 
— Extraction  of  metals  from  their  ores — The  properties  of  the 
metals — Compounds  of  the  metals — Chlorides — General  prop- 
erties of  the  chlorides — Oxidos — Hydroxides — Decomposition 
of  salts  by  acids  and  by  bases — Sulphides— Qualitative  an- 


xviii  CONTENTS. 


alysis — Hydrosulphides — Nitrates  —  Chlorates  —  Sulphates — 
Sulphites — Carbonates — Phosphates — Silicates — Reactions  in 
solution  are  reactions  of  ions 278 

CHAPTER  XX. 

THE    POTASSIUM    GROUP: 
LITHIUM,  SODIUM,  POTASSIUM,  CAESIUM,  RUBIDIUM    (AMMONIUM). 

( !  eneral — Potassium — Preparation — Properties — Compounds  of 
potassium — Potassium  iodide — Potassium  hydroxide — Potas- 
sium nitrate — Uses  of  potassium  nitrate — Gunpowder — Po- 
tassium chlorate — Properties — Uses — Potassium  cyanide — 
Potassium  sulphate  —  Sodium  —  Preparation  —  Properties  — 
Compounds  of  sodium — Sodium  chloride — Properties — Uses — 
Sodium  hydroxide — Sodium  nitrate — Sodium  sulphate — So- 
dium thiosulphate — Sodium  carbonate — The  Le  Blanc  pro- 
cess— The  Solvay  or  ammonia  process — Monosodium  carbon- 
ate, primary  sodium  carbonate — Disodium  phosphate — So- 
dium berate — Ammonium  salts — Ammonium  chloride — Am- 
monium sulphide — Ammonium  hydrosulphide — Sodium-am- 
monium phosphate — General  characteristics  of  the  metals  of 
the  alkalies — Rare  elements  of  the  group — Relations  between 
the  atomic  weights  of  the  members  of  this  group — Flame  re- 
actions— The  spectroscope 302 

CHAPTER  XXI. 

THE   CALCIUM   GROUP: 
CALCIUM,  BARIUM,  STRONTIUM,  GLUCINUM. 

General — Calcium— Compounds  of  calcium — Calcium  chloride 
— Calcium  oxide — Calcium  hydroxide — Uses — Calcium  car- 
bide —  Calcium  hypochlorite  —  Properties — How  bleaching- 
powder  acts  in  bleaching — Decomposition  of  bleaching-pow- 
der  by  boiling  its  solution — Uses — Calcium  carbonate — Tem- 
porary hardness — Calcium  sulphate — Permanent  hardness — 
Calcium  phosphates — Calcium  phosphate  essential  to  plant- 
growth — Artificial  fertilizers — Formation  of  calcium  phos- 
phate by  precipitation — Primary  calcium  phosphate — Cal- 
cium silicate — Glass — Mortar — Cements — Calcium  sulphide — 
Barium  and  strontium — Flame-reactions — Relations  between 
the  atomic  weights  of  the  members  of  this  group.. . , . . .  322 


CONTENTS.  xix 

CHAPTER  XXII. 

THE    MAGNESIUM    GBOUP : 
MAGNESIUM,  ZINC,  CADMIUM. 

PAGE 

Magnesium — Manufacture — Properties  —  Applications  —  Com- 
pounds of  Magnesium — Magnesium  oxide — Magnesium  chlo- 
ride— Magnesium  sulphate — Uses — Zinc — Metallurgy — Prop- 
erties— Applications — Alloys — Zinc  oxide — Zinc  sulphate — 
Zinc  chloride — Some  insoluble  compounds  of  zinc 339 

CHAPTER  XXIII. 

THE  COPPER  GROUP:     COPPER,  MERCURY,   SILVER. 

Copper — Metallurgy — Properties — Precipitation  of  copper — Ap- 
plications— Alloys — Compounds  of  copper — Copper  forms 
two  series  of  compounds — Cuprous  oxide — Cupric  oxide — 
Copper  sulphate — Copper  sulphide  —  Copper-plating  —  Mer- 
cury— Uses — Amalgams — Compounds  of  mercury — Mercuric 
oxide — Mercurous  chloride  —  Mercuric  chloride  —  Mercuric 
sulphide- — Precipitation  of  mercury  as  mercurous  chloride — 
Silver — Metallurgy  of  silver — Pattinson's  method  —  Zinc 
method  or  Parkes's  method — Amalgamation  process — Refin- 
ing of  silver — Properties — Alloys  of  silver — Compounds  of 
silver — Silver  nitrate — Applications  of  compounds  of  silver  in 
photography — Precipitation  of  metallic  silver — Insoluble  com- 
pounds of  silver — Argentous  and  argentic  compounds — The 
specific  heat  of  elements  as  a  means  of  determining  .their 
atomic  weights 346 

CHAPTER  XXIV. 

THE  ALUMINIUM   GROUP: 

JLLUMINIUM,  GALLIUM,  INDIUM, THALLIUM, SCANDIUM, YTTRIUM, 
LANTHANUM,  AND  YTTERBIUM. 

General — Aluminium — Preparation —Properties  —  Applications 
-Compounds  of  aluminium — Aluminium  oxide — Aluminium 
hydroxide— Alums — Aluminium  silicate — Natural  decompo- 
sition of  feldspar— Kaolin— Clay— Ultramarine— Porcelain- 
Earthenware — Action  of  soluble  carbonates  and  soluble  sul- 
phides on  solutions  of  aluminium  salts — Rare  elements  of  the 
aluminium  group • 361 


xx  CONTENTS. 

CHAPTER  XXV. 

THE   LEAD   GROUP: 
LEAD,,  TIN,   AND   GERMANIUM. 

PAGE 

General — Lead — Metallurgy — Properties — Uses — Compounds  of 
lead  and  oxygen — Lead  oxide — Lead  peroxide — Salts  of  lead 
— -Lead  acetate — Insoluble  salts  of  lead — Lead  carbonate — 
Lead  sulphide — Metallurgy  —  Properties  —  Uses  —  Alloys  — 
Stannous  and  stannic  compounds — Stannous  chloride — Stan- 
nic oxide — Metastannic  acid — Stannic  chloride — Stannic  sul- 
phide— How  to  distinguish  between  tin  and  other  metals.  . .  .  370 

CHAPTER  XXVI. 

THE  IRON  GROUP: 
IRON,    COBALT,    NICKEL. 

Iron — Occurrence — Metallurgy — Varieties  of  iron — Steel — Uses 
— Properties  of  iron — Iron  forms  two  series  of  compounds — 
Ferrous  compounds  are  converted  into  ferric  compounds  by 
oxidation — Ferrous  chloride — Ferrous  sulphate — Iron  alum — 
Ferrous  oxide — Ferric  oxide — Ferroso-ferric  oxide — Ferric 
acid — Sulphides  of  iron — Iron  pyrites,  or  pyrite — Nickel — 
Cobalt  379 

CHAPTER  XXWI. 

MANGANESE — CHROMIUM — URANIUM. 

Manganese — Compounds  of  manganese  with  oxygen — Compari- 
son of  manganese  with  aluminium  and  with  iron — Formation 
of  manganous  salts — Manganese  dioxide — Weldon's  process 
for  the  regeneration  of  manganese  dioxide  in  the  preparation 
of  chlorine — Potassium  permanganate — Reduction  of  potas- 
sium permanganate — Comparison  of  potassium  permangan- 
ate with  potassium  perchlorate — Chromium — Compounds  of 
chromium — Potassium  chromate — Potassium  dichromate — 
The  Chromate  and  dichromate  are  good  oxidizing  agents — In- 
soluble chromates — Chrome  alum — Comparison  of  chromium 
with  aluminium,  iron,  and  sulphur — Uranium — Radium  and 
Polonium  .,  .390 


CONTENTS.  xxi 

CHAPTER  XXVIII. 

PALLADIUM — PLATINUM — GOLD. 

PAGE 

Palladium — Platinum — Alloys  of  platinum — Chlorplatinic  acid 
— Gold — Forms  in  which  gold  occurs  in  nature — Metallurgy 
of  gold — Properties — Alloys  of  gold — Chlorides  of  gold 397 


CHAPTER  XXIX. 

V 

SOME   FAMILIAR  COMPOUNDS   OF   CARBON. 

Organic  chemistry — Occurrence  of  the  compounds  of  carbon — 
Formation  of  hydrocarbons — Distillation  of  coal — Distillation 
of  wood — Distillation  of  bones — Fermentation — Classes  of 
compounds  of  carbon — Compounds  of  carbon  and  hydrogen — 
Petroleum — Refining  of  petroleum — Hydrocarbons  in  petro- 
leum— Homology — The  ethylene  series  of  hydrocarbons — The 
acetylene  series — The  benzene  series — Marsh-gas,  methane, 
fire-damp — Substitution-products  of  the  hydrocarbons- 
Chloroform — lodoform — Ethylene,  olefiant  gas — Acetylene — 
Methyl  alcohol,  wood-spirit — Ethyl  alcohol,  spirits  of  wine — 
Different  kinds  of  fermentation — Distillation  of  fermented 
liquids — Properties  of  alcohol — Uses  of  alcohol — Glycerin — 
Properties — Acetic  aldehyde,  ordinary  aldehyde — Chloral — 
Formic  acid — Acetic  acid — Properties — Uses — Salts  of  acetic 
acid — Fatty  acids — Butyric  acid  —  Palmitic  acid  —  Stearic 
acid — Soaps — Use  of  soap — Action  of  soap  on  hard  waters — 
Relations  of  the  soap  industry  to  other  industries — Oxalic 
acid — Lactic  acid — Malic  acid — Tartaric  acid — Citric  acid — 
Ether — Action  of  acids  upon  alcohols — Saponification — Fats 
— Butter — Ethereal  salts  as  essences — Xitroglycerin — Com- 
parison of  formulas — Alcohols— More  complex  alcohols — 
Radicals  or  residues — Acids. .  403 


CHAPTER  XXX. 

V 

OTHER  COMPOUNDS  OF  CARBON. 

The  carbohydrates — Grape-sugar,  glucose,  dextrose — Formation 
of  dextrose — Manufacture  of  dextrose  or  glucose — Properties 
— Levtilose,  fruit-sugar — Cane-sugar — Sugar-refining — Molas- 
ses— Properties  of  sugar — Sugar  of  milk,  lactose — Souring  of 


xxii  CONTENTS. 

PAOK 

milk — Cellulose — Properties — Gun-cotton,  pyroxylin,  nitro- 
cellulose— Collodion — Celluloid — Paper — Starch  —  Manufact- 
ure of  starch — Properties — Flour — Bread-making — Aromatic 
compounds — Nitrobenzene — Aniline — Aniline  dyes  —  Phenol, 
carbolic  acid — Oil  of  bitter  almonds,  benzoic  aldehyde — Ben- 
zoic  acid — Balsams  and  odoriferous  resins — Gallic  acid — Tan- 
nic  acid,  tannin — Tanning — Indigo — Naphthalene — Anthra- 
cene— Alizarin — Glucosides — Myronic  acid — Alkaloids-— Qui- 
nine— Cocaine — Nicotine — Morphine 423 

CHAPTER  XXXI. 

QUALITATIVE  ANALYSIS. 

General — Examples  for  practice — List  of  substances  for  exam- 
ination— Study  of  Group  I — Study  of  Group  II — Study  of 
(Jroup  III— Study  of  Group  IV— Study  of  Group  V— Study 
of  Group  VI — General  directions — Classification  of  sub- 
stances studied 434 

APPARATUS  AND  CHEMICALS 447 

INDEX .  451 


AN  INTRODUCTION 

TO    THE 

STUDY    OF    CHEMISTRY. 

CHAPTER   I. 

CHEMICAL     ACTION.  —  ELEMENTS.  —  COMPOUNDS.  — 
HOW   TO    STUDY   CHEMISTRY. 

Introductory. — Those  things  which  are  most  familiar  to 
us  are  apt  to  be  regarded  with  least  wonder  and  to  occasion 
the  least  thought.  Take,  for  example,  the  changes  in- 
cluded under  the  head  of  fire.  Unless  we  have  studied 
these  changes  with  care,  what  can  we  make  of  them  ?  We 
see  substances  destroyed  by  fire.  They  disappear  for  the 
most  part.  We  feel  the  heat  produced  by  the  burning. 
We  know  that  this  heat  disappears,  and  we  have  little  left 
in  the  place  of  the  substance  burned.  Take,  as  another 
example,  the  rusting  of  iron.  We  all  know  that  iron  when 
exposed  to  moist  air  undergoes  a  serious  change,  becoming 
covered  with  a  reddish-brown  substance  called  rust.  If 
the  piece  of  iron  is  comparatively  thin,  and  it  is  allowed 
to  lie  in  the  air  long  enough,  it  will  be  completely  changed 
to  the  reddish-brown  substance,  and  no  iron  as  such  will 
be  left.  If  a  spark  is  brought  in  contact  with  gunpowder 
there  is  a  flash  and  the  powder  disappears,  dense  smoke 
appearing  in  its  place.  What  are  the  causes  of  these 
remarkable  changes,  ?  Can  we  learn  anything  about  them 
>y  study  ? 


2  INTRODUCTION   TO   CHEMISTRY. 

Chemical  Changes, — In  those  changes  which  have  been 
referred  to,  the  substances  changed  disappear  as  such. 
After  the  fire,  the  wood  or  the  coal,  or  whatever  may  have 
been  burned,  is  no  longer  to  be  found.  The  gunpowder 
after  the  flash  is  no  longer  gunpowder.  The  rusted  iron 
is  no  longer  iron,  and,  no  matter  how  long  the  rust  may 
be  allowed  to  lie  unmolested,  it  will  not  return  to  the  form 
of  iron.  Iron  may,  further,  be  changed  by  contact  with 
other  substances  than  air  so  as  to  lose  its  properties. 
Strong  vinegar,  which  contains  the  substance  known  to 
chemists  as  acetic  acid,  acts  upon  iron,  causing  it  to  lose 
its  characteristic  properties.  The  substances  known  as 
muriatic  or  hydrochloric  acid,  nitric  acid,  and  sulphuric 
acid  also  act  upon  iron  and  give  rise  to  the  formation  of 
new  substances  which  have  not  the  properties  of  iron. 
Changes  of  this  kind  in  which  the  substances  disappear 
and  something  else  is  formed  in  their  place  are  known  as 
chemical  changes,  and  chemistry  is  the  science  which  has 
to  deal  with  changes  in  the  composition  of  substances. 

Physical  Changes. — There  are  many  changes  taking 
place  which  do  not  affect  the  composition  of  substances. 
Iron,  for  example,  may  be  changed  in  many  ways  and  still 
remain  iron.  It  may  become  hotter  or  colder.  Its  posi- 
tion may  be  changed.  The  difference  between  a  piece  of 
iron  moving  and  a  piece  at  rest  is  a  very  wonderful  one, 
though  we  are  not,  as  a  rule,  much  impressed  by  the 
difference.  The  iron  may  be  struck  in  such  a  way  as  to 
cause  it  to  give  forth  a  sound.  AVhile  giving  forth  the 
sound  its  condition  is  certainly  different  from  that  in  which 
it  does  not  give  forth  sound.  The  iron  may  be  made  so 
hot  that  it  gives  light.  A  piece  of  iron  may  be  changed 
further  by  connecting  it  with  what  is  known  as  a  galvanic 
battery.  We  can  easily  recognize  the  difference  between 
a  piece  of  iron  tfirpvigh.  which  Jar  fcrttfcrfent  of  electricity  is 


PHYSICS  AND   CHEMISTRY.  3 

passing  and  one  through  which  no  current  is  passing. 
Finally,  when  a  piece  of  iron  is  brought  in  contact  with  a 
piece  of  loadstone,  it  acquires  new  properties.  It  now 
has  the  power  to  attract  and  hold  to  itself  other  pieces  of 
iron.  In  all  these  cases,  then,  the  iron  is  changed,  but  it 
remains  iron.  After  the  moving  iron  comes  to  rest  it  is 
exactly  the  same  thing  that  it  was  before.  After  the  iron 
which  is  giving  forth  sound  has  ceased  to  give  forth 
sound,  it  returns  to  its  original  condition.  Let  the  heated 
iron  alone  and  it  cools  down,  ceasing  soon  to  give  off  light, 
and  giving  no  evidence  of  being  warm.  Remove  the  iron 
from  contact  with  the  galvanic  battery  and  it  loses  those 
properties  which  are  due  to  the  current  of  electricity.  In 
time,  the  iron  which  is  magnetized  by  contact  with  the 
loadstone  loses  its  magnetic  properties.  Such  changes  are 
called  physical  changes. 

Physics  and  Chemistry. — From  what  has  been  said  in 
regard  to  the  kinds  of  change  which  iron  can  undergo,  it 
will  be  seen  that  these  changes  are  of  two  kinds : 

1st.   Those  which  do  not  permanently  affect  the  iron. 

2d.  Those  which  do  permanently  affect  the  iron  and 
which  necessarily  cause  the  formation  of  new  substances 
with  properties  quite  different  from  those  which  belong  to 
the  iron.  What  is  true  of  iron  is  true  in  general  of  all 
other  substances.  We  therefore  have  two  classes  of 
changes  presented  to  us  for  study: 

1st.  Those  which  do  not  affect  the  composition  of  sub- 
stances. 

3d.  Those  which  affect  the  composition  of  substances 
and  give  rise  to  the  formation  of  new  substances  with  new 
properties. 

Changes  of  the  first  kind  are  called  physical  changes. 
Those  of  the  second  kind  are  called  chemical  changes. 

That   branch    of   knowledge    which    has   to    deal   with 


4  INTRODUCTION    TO   CHEMISTRY. 

physical  changes  is  known  as  PHYSICS;  and  that  which 
has  to  deal  with  chemical  changes  is  known  as  CHEMISTRY. 
Everything  that  has  to  do  with  motion,  with  heat,  light, 
sound,  electricity,  and  magnetism,  is  studied  under  the 
head  of  Physics.  Everything  that  has  to  do  with  the  com- 
position of  substances  and  changes  in  the  composition  is 
studied  under  the  head  of  Chemistry. 

EXPERIMENT  1.— Hold  a  piece  of  platinum  wire  in  the  flame  of 
the  laboratory  burner  for  a  moment.  Remove  it  and  hold  it  for 
a  few  moments  in  the  air.  What  kind  of  change  did  it  undergo 
in  the  flame  ?  Hold  a  piece  of  magnesium  ribbon  in  the  flame  by 
means  of  a  pair  of  pincers.  What  kind  of  change  takes  place  ? 
Give  reasons  for  your  conclusions. — Mention  some  phenomena 
familiar  to  you  that  further  illustrate  these  two  kinds  of  change. 

Relations  between  the  Different  Kinds  of  Change.— 
Although  at  first  sight  the  different  kinds  of  change 
referred  to  appear  to  be  quite  distinct  from  one  another, 
they  are,  in  reality,  closely  related.  If  a  body  in  motion 
is  stopped  suddenly,  it  becomes  hot.  Many  examples  of  a 
similar  transformation  of  motion  into  heat  are  familiar :  a 
wire  becomes  hot  when  hammered  on  an  anvil;  a  coin 
rubbed  on  cloth  becomes  hot.  In  both  cases  the  cause  of 
the  heat  is  the  interference  with  the  motion.  The  hammer 
is  stopped  and  becomes  hot;  the  coin  is  not  stopped,  but 
the  motion  is  interfered  with,  and  we  have  to  push  harder 
in  order  to  move  it  over  the  cloth  than  we  should  to  move 
it  in  the  air.  A  wire  through  which  a  current  of  electricity 
is  passing  is  heated,  and  if  the  wire  is  small  and  the  current 
strong  it  will  become  so  hot  that  it  will  give  off  light. 
Here  the  electricity  causes  heat  and  light.  Again,  we 
know  that  by  means  of  heat  we  can  produce  motion.  The 
steam-engine  is  the  best  example  of  this  kind  of  trans- 
formation. We  build  a  fire;  this  heats  the  water  in  the 
boiler;  the  water  is  converted  into  steam,  which  expands 
and  moves  the  piston;  and  the  motion  of  the  piston  is  the 


CHEMICAL   CHANGES   CAUSED  BY  HEAT.  5 

seat  of  all  the  complex  motions  that  take  place  in  the 
different  parts  of  the  engine.  The  train  or  the  ship 
moves.  What  moves  it  ?  Plainly,  the  heat  is  the  cause 
of  the  motion.  But  we  can  go  a  step  farther  back  and  ask 
what  causes  the  heat.  The  answer  is  obvious.  It  is  the 
burning  of  the  fuel.  But,  in  burning,  the  composition  of 
the  fuel  is  completely  changed.  A  change  is  produced 
which  in  itself  is  not  heat.  When  a  piece  of  coal  burns, 
then,  it  is  undergoing  a  change  in  composition,  and,  as  a 
result  of  this  change,  heat  is  produced.  The  heat  is, 
therefore,  produced  by  a  chemical  change  in  the  coal,  and 
we  may  say  that  the  motion  of  the  steam-engine  is  the 
result  of  the  chemical  change  taking  place  in  the  coal  or 
wood  which,  in  burning,  produces  the  heat. 

Chemical  Changes  caused  by  Heat.  —  Just  as  in  all 
ordinary  fires  we  have  heat  produced  as  a  result  of  chemi- 
cal changes  in  the  fuel,  so  we  may  have  chemical  changes 
produced  by  heat  or  by  electricity. 

EXPERIMENT  2. — In  a  clean,  dry  test-tube  put  enough  white 
sugar  to  make  a  layer  i  to  £  an  inch  thick. 
Hold  the  tube  in  the  flame  of  a  spirit-lamp  or 
a  laboratory  burner,  as  shown  in  Fig.  1. — De- 
scribe what  takes  place.  What  is  the  appear- 
ance of  the  substances  left  in  the  tube  ?  Is 
there  any  sugar  left?  After  dooling,  taste 
the  mass. 

EXPERIMENT  3.— From  a  piece  of  hard  glass 
tubing  of  about  6  to  7  millimetres  (£  inch) 
internal  diameter  cut  off  a  piece  about  10 
centimetres  (4  inches)  long  by  making  a  mark 
across  it  with  a  triangular  file,  and  then  seiz- 
ing it  with  both  hands,  one  on  each  side  of 
the  mark,  pulling  and  at  the  same  time  press-  FlG- 1- 

ing  slightly  as  if  to  break  it.  Clean  and  dry  it,  and  hold  one  end 
in  the  flame  of  a  laboratory  burner  until  it  melts  together.  Dur- 
ing the  melting  turn  the  tube  constantly  around  its  long  axis  so 


0  INTRODUCTION    TO   CHEMISTRY. 

that  the  heat  may  act  uniformly  upon  it.  Put  into  it  enough 
red  oxide  of  mercury  (mercuric  oxide)  to  form  a  layer  about  12 
millimetres  (£  inch)  thick.  Heat  the  tube  as  in  the  last  experi- 
ment. During  the  heating  thrust  into  the  tube  a  splinter  of  wood 
which  has  a  spark  on  the  end.  Take  it  out  and  put  it  back  again 
a  number  of  times.  What  changes  do  you  observe  in  the  sub- 
stance in  the  tube  ?  What  takes  place  when  the  splinter  with 
the  spark  is  thrust  into  the  tube  ? 

Electric  Currents  connected  with  Chemical  Changes.— 

In  a  galvanic  battery  there  are  always  substances  which 
are  undergoing  changes  in  composition,  and  the  electric 
current  is  connected  with  these  changes.  A  simple  form 
of  a  battery  is  represented  in  Fig.  2. 

The  plates  marked  K  are  of  copper,  those  marked  Z  of 
zinc.  The  plates  are  connected  together  by  wires,  as 
shown.  In  each  vessel  there  is  poured  a  mixture  of  sul- 


FIG.  2. 

phuric  acid  and  water.  This  mixture  acts  upon  the  zinc, 
producing  a  chemical  change  in  it.  The  wire  connecting 
the  last  plate  of  copper  with  the  first  plate  of  zinc  is  found 
to  have  an  electric  current  passing  through  it.  This  wire 
not  only  conducts  the  electric  current,  but  also  becomes 
heated. 

Chemical  Changes  connected  with  the  Passage  of  the 
Electric  Current. — This  may  be  well  illustrated  by  the 
action  of  an  electric  current  on  water. 

EXPERIMENT  4. — To  the  ends  of  the  copper  wires  connected  with 
two  cells  of  a  Bunsen's  or  Grove's  battery  fasten  small  platinum 


TWO   GASES  FORMED. 


plates  say  25  min.  (1  inch)  long  by  12  mm.  (£  inch)  wide.  Insert 
these  platinum  electrodes  into  water  contained  in  a  small  shallow 
glass  vessel  about  15  cm.  (6  inches)  wide  and  7  to  8  cm.  (3  inches) 
deep,  taking  care  to  keep  them  separated  from  each  other.  No 
action  will  take  place,  for  the  reason  that  water  will  not  conduct 
the  current,  and  hence  when  the  platinum  electrodes  are  kept 
apart  there  really  is  no  current.  By  adding  to  the  water  about 
one  tenth  its  own  volume  of  strong  sulphuric  acid,  it  acquires 
the  power  to  convey  the  current.  It  will  then  be  observed  that 
bubbles  rise  from  each  of  the  platinum  plates.  In  order  to  collect 
them  an  apparatus  like  that  shown  in  Fig.  3  may  be  used. 

h  and  o  represent  glass  tubes  which 
may  conveniently  be  about  30  cm.  (1  foot) 
long  and  25  mm.  (1  inch)  internal  diam- 
eter. They  are  first  filled  with  the  water 
containing  one  tenth  its  volume  of  sul- 
phuric acid,  and  then  placed  with  the 
mouth  under  water  in  the  vessel  A.  The 
platinum  electrodes  are  now  brought 
beneath  the  inverted  tubes.  The  bubbles 
which  rise  from  them  will  pass  upward  in 
the  tubes,  and  the  water  will  be  pressed 
down.  Gradually  the  water  will  be  com- 
pletely forced  out  of  one  of  the  tubes, 
while  the  other  is  still  half  full  of  water. 
The  substances  thus  collected  in  each  of 
the  tubes  are  invisible  gases.  After  the 
first  tube  is  full  of  gas,  place  the  thumb 
over  its  mouth  and  remove  the  tube. 
Turn  it  mouth  upward  and  at  once  apply 
a  lighted  match  to  it.  What  takes  place  ? 

"Was  the  gas  in  the  tube  ordinary  air  ?  In  the  mean  time  the 
second  tube  will  have  become  filled  with  gas.  Remove  this  tube 
in  the  same  way  and  insert  a  thin  piece  of  wood  with  a  spark  on 
it.  What  do  you  observe  ?  In  what  experiment  already  per- 
formed have  you  observed  something  very  much  like  this  ? 

Two  Gases  Formed. — Without  going  into  further  details, 
it  is  clear  from  this  experiment  that  when  an  electric  cur- 
rent acts  on  water  containing  some  sulphuric  acid  two 


Fia.  3. 


INTRODUCTION    TO   CHEMISTRY. 

invisible  gases  are  produced.  We  shall  have  occasion  here- 
after to  stud}'  this  experiment  much  more  carefully,  and 
we  shall  find  that  from  it  we  can  learn  a  great  deal  more 
than  we  have  just  learned. 

Electrolysis. — Such  a  process  as  that  shown  in  the  last 
experiment  is  called  electrolysis.  The  ends  of  the  wires 
connected  with  the  battery  are  called  electrodes.  That 
electrode  which  is  connected  with  the  negative  or  zinc 
pole  of  the  battery  is  called  the  negative  electrode  or 
cathode  ;  while  that  electrode  which  is  connected  with  the 
positive  pole  of  the  battery  is  called  the  positive  pole  or 
anode. 

Collection  of  Gases. — As  it  is  frequently  necessary  in 
studying  chemical  changes  to  deal  with  gases,  it  will  be 
well  at  this  point  for  the  student  to  familiarize  himself 
with  the  method  adopted  for  collecting  gases. 

EXPERIMENT  5. — Fill  a  test-tube  or  glass  cylinder  with  water  ; 
close  the  mouth  with  the  thumb  or  a  ground-glass  plate  ;  invert 


FIG.  4. 


the  tube,  and  put  the  mouth  under  water.     The  water  stays  in 
the  tube   after  the  thumb  or  glass  plate  is  removed.     (Why  ?) 


RELATION  BETWEEN  CHEMISTRY  AND  PHYSICS.         9 

Now  take  a  piece  of  glass  or  rubber  tubing  ;  put  one  end  under 
the  mouth  of  the  inverted  tube,  and  blow  gently  through  the 
other  end.  Bubbles  will  rise  in  the  tube  and  the  water  will  be 
displaced.  In  this  case  the  gases  from  the  lungs  are  collected. 
When  they  come  below  the  mouth  of  the  tube,  being  lighter  than 
water,  they  rise,  and  as  the  space  occupied  by  them  cannot  be 
occupied  by  the  water  too,  the  latter  is  displaced.  (See  Fig.  4.) 

EXPERIMENT  6. — To  transfer  a  gas  from  one  vessel  to  another 
by  displacement  of  water,  place  both  vessels  inverted  in  the  same 
bath,  and  then  gradually  bring  the  one  containing  the  gas,  mouth 
upward,  below  the  one  containing  the  water.  (See  Fig.  5.) 

Relation  between  Chemistry  and  Physics. — The  experi- 
ments performed  will  suffice  to  show  that  the  different 
kinds  of  changes,  both  the  physical  and  the  chemical,  are 
more  closely  related  to  one  another  than  they  appear  to 
be  at  first  sight.  In  consequence  of  this  relation  we 
cannot  deal  with  chemical  changes  without  constantly 
having  to  deal  with  physical  changes.  For  a  thorough 
understanding  of  chemical  changes  it  is  necessary  to  have 
some  knowledge  of  the  changes  produced  by  heat  and 


FIG.  5. 

electricity.  It  will  be  found  that  whenever  chemical 
changes  take  place,  heat  changes  and  sometimes  electric 
changes  also  take  place.  And  it  will  be  found,  too,  that, 
in  order  to  bring  about  chemical  changes,  use  is  frequently 
made  of  heat  and  electricity.  If,  therefore,  the  student 
has  not  studied  physics,  he  should  familiarize  himself  with 
a  few  of  the  elementary  facts  of  the  science  before  under- 


io  INTRODUCTION   TO   CHEMISTRY.    * 

taking  the  study  of  chemistry.  He  should  know  what 
physical  changes  can  be  produced  by  heat ;  what  boiling 
is;  what  evaporation  is;  what  "condensing  a  vapor" 
means;  what  the  expression  "to  pass  an  electric  current'' 
means;  how  the  more  common  forms  of  galvanic  batteries 
are  made,  etc.,  etc.  All  these  matters  are  of  importance 
in  studying  chemical  changes,  and  still  a  text-book  of 
chemistry  is  not  the  proper  place  to  treat  of  them.  It 
will  therefore  be  assumed  that  the  student  has  this  knowl- 
re. 


Object  of  the  Chemist's  Study. — Everything  that  has  to 
do  with  the  composition  of  substances  is  the  object  of  the 
chemist's  study.  Most  substances  can  by  proper  methods 
be  separated  into  simpler  ones,  and  these  again  into  still 
simpler  ones  which  cannot  be  further  decomposed  by  any 
means  known  to  us.  Substances  that  cannot  be  decom- 
posed into  simpler  ones  by  us  are  called  elements.  Now, 
although  there  are  thousands  of  different  substances,  these 
are  really  made  up  of  a  comparatively  small  number  of 
elements.  The  number  of  elements  thus  far  discovered  is 
between  seventy  and  eighty,  but  most  of  these  are  rare. 
We  shall  find  that  most  things  we  have  to  deal  with  are 
made  up  of  about  a  dozen  elements,  and  that  most  of  the 
chemical  changes  that  are  taking  place  around  us,  and 
that  we  need  to  study  in  order  to  get  an  insight  into  the 
nature  of  chemical  action,  take  place  between  this  small 
number  of  elements. 

Mechanical  Mixtures. — Most  of  the  substances  found  in 
nature  are  made  up  of  several  others.  Wood,  for  example, 
is  very  complex,  containing  a  large  number  of  distinct 
substances  intimately  mixed  together.  Some  of  these  can 
be  isolated,  but  it  is  impossible  to  isolate  them  all  with  the 
means  at  present  at  our  command.  Most  rocks  are  also 
quite  complex,  and  it  is  a  difficult  matter  to  isolate  the 


MECHANICAL   MIXTURES.  II 

constituents.  If  we  examine  a  piece  of  coarse-grained 
granite  we  see  plainly  enough  that  it  contains  different 
things  mixed  together,  and  if  it  is  broken  up  we  can  pick 
out  pieces  of  different  substances  from  the  mass.  If  we 
now  examine  a  piece  of  each  of  the  different  substances,  it 
appears  to  be  homogeneous,  i.e.,  we%annot  recognize  the 
presence  of  more  than  one  kind  of  thing  in  any  one  piece. 
If  the  piece  is  powdered,  some  of  the  powder  can  be 
examined  with  a  microscope  without  the  presence  of  more 
than  one  substance  being  recognized.  We  are  able  to 
isolate  three  substances  from  granite  by  simply  breaking 
it  up.  We  might  therefore  conclude  that  granite  consists 
of  three  substances.  This  is  true,  but  it  is  not  the  whole 
truth.  For  it  is  possible  to  get  simpler  substances  from 
each  of  the  three.  This,  however,  is  a  much  more  difficult 
process  than  the  separation  first  accomplished.  Sub- 
stances must  be  brought  in  contact  with  each  of  the  three 
constituents  which  change  their  composition,  i.e.,  act 
chemically  upon  them,  and  high  heat  must  be  used  to  aid 
the  action.  It  is  thus  possible  to  separate  the  three  com- 
ponents of  granite  into  their  elements. 

Substances  may  then  be  united  in  different  ways.  They 
may  be  so  united  that  it  is  a  simple  thing  to  separate  them 
by  mechanical  processes.  Or  they  may  be  so  united  that 
it  is  impossible  to  separate  them  by  mechanical  processes. 
By  a  mechanical  process  is  meant  any  process  that  does 
not  involve  the  use  of  heat,  electricity,  or  chemical  action. 
Thus,  the  mechanical  process  made  use  of  in  the  case  of 
granite  consisted  in  picking  out  the  pieces. 

EXPERIMENT  7. — Mix  a  gram  or  two  of  powdered  roll-sulphur 
and  an  equal  weight  of  very  fine  iron  filings  in  a  small  mortar. 
Examine  a  little  of  the  mixture  with  a  microscope.  Do  you  see 
both  the  sulphur  and  the  iron  ? 

EXPERIMENT  8. — Pass  a  small  magnet  through  the  mixture  above 
prepared.  Unless  the  substances  used  are  thoroughly  dry,  parti- 


12  INTRODUCTION    TO   CHEMISTRY. 

cles  of  sulphur  will  adhere  to  the  magnet,  but  even  then  it  will  be 
seen  that  most  of  that  which  is  taken  out  of  the  mixture  is  iron. 
This  separation  is  a  mechanical  separation.  It  is  a  somewhat 
more  refined  method  of  picking  out  than  that  referred  to  in  the 
case  of  the  granite. 

EXPERIMENT  9. — Pour  a  few  cubic  centimetres  of  carbon  bisul- 
phide on  a  little  powdered  roll-sulphur  in  a  dry  test-tube.  Filter 
and  let  the  solution  evaporate  on  a  watch-glass.  What  takes 
place  ?  In  a  second  tube  treat  iron  filings  in  the  same  way.  Filter 
and  evaporate.  What  takes  place  ?  Now  in  a  third  tube  treat 
a  small  quantity  of  a  mixture  with  carbon  bisulphide.  After 
shaking  for  some  time  let  the  tube  stand  quietly  so  that  any  solid 
suspended  in  the  liquid  may  settle  to  the  bottom.  Then  pass  the 
liquid  through  a  dry  filter  into  a  watch-glass.  Let  this  watch- 
glass  stand  until  the  liquid  has  evaporated.  Examine  what  re- 
mains undissolved  in  the  test-tube.  After  the  liquid  has  evap- 
orated examine  what  is  left  on  the  watch-glass.  What  is  in  the 
test-tube  ?  What  on  the  watch-glass  ?  Explain  what  has  taken 
place. 

EXPERIMENT  10. — Make  a  fresh  mixture  of  three  grams  each  of 
powdered  roll-sulphur  and  fine  iron  filings.  Grind  them  together 
very  intimately  in  a  dry  mortar  and  put  them  in  a  small  dry  test- 
tube.  Heat  sharply  until  the  mass  begins  to  glow,  then  take  the 
tube  out  of  the  flame.  After  the  mass  has  become  cool,  break 
the  tube,  and  put  the  contents  in  a  mortar.  Break  up  the  solid 
and  examine  it.  Compare  it  with  the  original  mixture.  Treat 
each  with  hydrochloric  acid.  Are  they  identical  ? 

The  Product  is  a  Chemical  Compound. — The  new  sub- 
stance formed  by  the  action  of  heat  on  the  mixture  of 
sulphur  and  iron  is  no  longer  a  mechanical  mixture.  It 
cannot  be  decomposed  by  a  mechanical  process.  The  con- 
stituents are  much  more  firmly  united  than  they  were  in 
the  mixture.  They  have  lost  their  identity.  They  are 
both  present,  to  be  sure,  but  by  means  of  an  ordinary 
examination  we  cannot  recognize  them,  as  their  character- 
istic properties  have  been  lost.  When  the  mixture  began 
to  glow,  the  act  of  combination  began,  and  the  glowing 
was  a  result  of  the  act  of  combination.  The  sulphur  and 


A   CHARACTERISTIC  Oh'  CHEMICAL   ACTION.          13 

iron  combined  with  each  other  chemically,  and  formed  a 
chemical  compound.  They  did  not  act  upon  each  other 
when  simply  brought  in  contact.  It  was  necessary  to  heat 
the  mixture  in  order  to  cause  chemical  combination  to 
take  place.  The  heat  in  this  case  helped  the  chemical 
action.  Bat  after  the  action  began  it  continued  without 
further  aid  and  produced  heat,  as  was  shown  by  the  glow- 
ing of  the  mass. 

One  of  the  Chief  Characteristics  of  Chemical  Action. — 
The  essential  feature  of  the  action  in  the  case  of  iron  and 
sulphur,,  just  studied,  is  this: 

The  substances  -which  act  upon  each  other  lose  their  indi- 
vidual properties  and  something  is  formed  with  entirely 
new  properties.  - 

This  is  true  of  every  case  of  chemical  action,  and  it  is 
one  of  the  chief  characteristics  of  that  kind  of  action. 
If  we  should  examine  a  number  of  cases  of  chemical 
action,  we  might  be  inclined  to  think  that  they  had  no 
common  features  ;  but  this  loss  of 'properties  and  the  for- 
mation of  new  substances  always  take  place.  A  few  ex- 
amples will  help  to  emphasize  this  truth. 

EXPERIMENT  11.— Examine  a  piece  of  calc-spar  or  of  marble. 
Describe  it.  Heat  a  piece  in  a  small  glass  tube,  as  in  Experiment 
3.  Does  it  melt  ?  Put  a  piece  the  size  of  a  pea  in  a  test-tube 
with  distilled  water.  Thoroughly  shake,  and  then,  as  heating 
usually  aids  solution,  boil.  Now  pour  off  a  few  drops  of  the 
liquid  on  a  piece  of  platinum  *  foil  or  an  evaporating-dish,  and 
by  gently  heating  cause  the  water  to  evaporate.  If  there  is  any- 
thing solid  in  solution  there  will  be  a  residue  on  the  platinum 
foil  or  evaporating-dish.  If  not,  there  will  be  no  residue.  Is  the 
substance  soluble  in  water  ?  Now  treat  a  small  piece  of  the  sub- 
stance with  dilute  hydrochloric  acid  and  notice  what  takes  place. 

*  Platinum,  an  expensive  metal,  finds  extensive  use  in  chemicvil 
laboratories,  for  the  reason  that  it  resists  the  action  of  heat  and  of 
most  chemical  substances. 


INTRODUCTION    TO   CHHMISTRY. 


After  the  action  has  continued  for  about  a  minute,  insert  a  lighted 
match  in  the  upper  part  of  the  tube.  What  takes  place  ?  Does 
the  calc-spar  dissolve  ?  To  determine  whether  anything  else  has 
taken  place,  we  shall  have  to  get  rid  of  the  excess  of  hydrochloric 
acid.  This  we  can  easily  do  by  boiling  it,  when  it  passes  off  in 
the  form  of  vapor,  and  then  whatever  is  in  solution  will  remain 
behind.  For  this  purpose  put  the  solution  in  a  small,  clean  por- 
celain evaporating-dish,  and  put  this  on  a  vessel  containing  boil- 
ing water,  or  a  water-bath.  The  operation  should  be  carried  on 
in  a  place  in  which  the  draught  is  good,  so  that  the  vapors  will 
not  collect  in  the  working-room.  They  are  not  poisonous,  but 
they  are  annoying.  The  arrangement  for  evaporating  is  repre- 
sented in  Fig.  6. 

After  the  liquid  has  evaporated  and  the  substance  in  the 
evaporating-dish  is  dry,  examine  it  and  carefully  compare  its 
properties  with  those  of  the  substance  which  was  put  into  the 
test-tube.  How  does  it  differ  in  appearance  from  this  ?  Is  it 
harder  or  softer  ?  Is  it  soluble  in  water  ?  Does  it  melt  when 
heated  in  a  dry  tube?  Does  it  give  off  bubbles  of  gas  when 
treated  with  hydrochloric  acid  ?  Let  some  of  it  stand  in  contact 
with  the  air.  What  change  takes  place  ? 

What  this  Experiment  Shows. — The  experiment  shows 
that  when  hydrochloric  acid  acts  upon  calc-spar  or  marble, 

the  latter  at  least  loses  its  own 
properties.  It  might  be  shown 
that  some  of  the  hydrochloric 
acid  also  loses  its  properties. 
In  place  of  the  two  we  get  a 
new  substance  with  entirely 
different  properties.  The  two 
substances  have  acted  chemi- 
cally upon  each  other  and  pro- 
duced a  chemical  compound 
different  from  either.  In  this 
case  it  was  only  necessary  to 
bring  the  substances  in  contact 
in  order  to  cause  them  to  art  chemically  upon  each  other. 


FIG.  G. 


GENERAL   CONCLUSION.  15 

It  was  not  necessary  to  heat  them,  as  it  was  in  the  case  of 
the  iron  and  sulphur. 

EXPERIMENT  12.— Bring  together  in  a  test-tube  a  few  small 
pieces  of  copper  and  some  moderately  dilute  nitric  acid.  What 
takes  place  ?  Do  not  inhale  the  gas.  Describe  the  changes  in 
the  color  of  the  liquid.  Does  the  copper  dissolve  ?  Examine  this 
0O  dilution,  as  in  Experiment  11,  and  see  what  has  been  formed. 
.What  are  the  properties  of  the  substance  found  after  evaporation 
of  the  liquid?  Is  it  colored?  Is  it  soluble  in  water?  Does  it 
change  when  heated  in  a  tube  ?  Is  it  hard  or  soft  ?  Does  it  in 
any  way  suggest  the  copper  with  which  you  started  ? 

EXPERIMENT  13. — Try  the  action  of  dilute  sulphuric  acid  on  a 
little  zinc  in  a  test-tube.  Apply  a  lighted  match  to  the  moutli  of 
the  tub4T'^)oes  the  result  suggest  anything  noticed  in  an  experi- 
ment already  performed  ?  What  is  the  meaning  of  the  bubbling 
of  the  liquid  ?  After  the  zinc  has  disappeared  evaporate  the 
solution  as  in  Experiments  11  and  12.  Carefully  compare  the 
properties  of  the  substance  left  behind  with  those  of  zinc. 

EXPERIMENT  14. — Hold  the  end  of  a  piece  of  magnesium  ribbon 
about  20  centimetres  (8  inches)  long  in  a  flame  until  it  takes  fire  ; 
then  hold  the  burning  substance  quietly  over  a  piece  of  dark 
paper,  so  that  the  light,  white  product  may  be  collected.  Compare 
the  properties  of  this  white  product  with  those  of  the  magnesium. 
Here  again  a  chemical  act  has  taken  place.  The  magnesium  has 
combined  with  something  from  the  air,  and  heat  was  produced  by 
the  combination.  The  product  is  the  white  substance  (compare 
Exp.  1). 

EXPERIMENT  15.— In  a  small,  dry  flask  (400  to  500  ccm.)put  a 
bit  of  granulated  tin.  Pour  upon  it,  2  or  3  ccm.  concentrated 
nitric  acid.  If  no  change  takes  place,  heat  gently  and.  presently 
there  will  be  a  copious  evolution  of  a  reddish-brown  gas  with  a 
disagreeable  smell.  (Under  what  conditions  has  a  gas  like  this 
already  been  obtained  ?)  What  appears  in  place  of  the  tin  ?  Com- 
pare the  properties  of  the  new  substance  with  those  of  tin.  Why 
are  you  justified  in  concluding  that  they  are  not  the  same  thing  ? 

General  Conclusion, — Experiments  like  those  just  per- 
formed might  be  multiplied  to  any  extent  desired.  But 


1 6  INTRODUCTION   TO   CHEMISTRY. 

a  sufficient  number  have  already  been  studied  to  show  upon 
what  kinds  of  observations  is  based  the  statement  that : 

Whenever  two  or  more  substances  act  upon  one  another 
chemically  they  lose  their  characteristic  properties,  and  new 
substances  with  new  properties  are  formed. 

The  Cause  of  Chemical  Action, — It  is  evident  from  what 
has  already  been  learned  that  there  is  some  power  that  can 
hold  substances  together  in  a  very  intimate  way,  so  intimate 
that  they  cannot  be.  recognized  by  ordinary  means.  We 
do  not  know  what  causes  the  sulphur  and  iron  to  combine, 
but  we  know  that  they  do  combine.  Similarly,  we  do  not 
know  what  causes  a  stone  thrown  upward  in  the  air  to  fall 
back  again,  but  we  know  that  it  falls  back.  It  is  true,  we 
may  say  and  do  say  that  the  cause  of  the  falling  of  the 
stone  is  the  attraction  of  gravitation,  but  this  does  not  give 
us  any  information,  for  if  we  ask  what  the  attraction  of 
gravitation  is,  we  can  only  answer  that  it  is  that  which 
causes  all  bodies  to  attract  one  another.  We  can  also  give 
a  name  to  that  which  causes  chemical  combination,  but 
this  would  not  help  us  to  understand  what  this  cause  is. 
All  the  chemical  changes  that  are  taking  place  around 
us  may  be  referred  to  this  cause,  whatever  it  may  be.  If 
this  cause  should  suddenly  cease  to  operate,  what  would 
be  the  result  ?  Nature  would  be  infinitely  less  complex 
than  it  now  is.  All  substances  now  known  to  be  chemical 
compounds  would  be  resolved  into  the  elements  of  which 
they  are  composed,  and,  as  far  as  we  know,  there  would  be 
but  about  seventy  or  eighty  different  kinds  of  substances. 
All  living  things  would  cease  to  exist,  and  in  their  place 
we  should  have  three  invisible  gases,  and  something  very 
much  like  charcoal.  Mountains  would  crumble  to  pieces. 
All  water  would  disappear,  giving  two  invisible  gases. 
The  processes  of  life  in  its  many  forms  would  be  impossi- 
ble, for,  however  subtle  that  which  we  call  life  may  be,  we 

\ 


HOW   TO  STUDY  CHEMISTRY.  17 

cannot  imagine  it  to  exist  without  the  existence  of  certain 
complex  forms  of  matter;  and,  as  regards  the  life -processes 
of  larger  animals  and  plants,  most  complex  chemical 
changes  are  constantly  taking  place  within  them,  and  these 
changes  are  absolutely  essential  to  the  continuation  of  life. 

Summary. — We  have  thus  far  learned  the  difference 
between  physical  and  chemical  change.  We  have  learned 
the  difference  between  elements  and  chemical  compounds, 
and  between  chemical  compounds  and  mechanical  mix- 
tures. We  have  learned  that  there  is  a  close  relation 
between  the  different  kinds  of  physical  change  and  chemi- 
cal change;  and  that  one  kind  of  change  is  capable  of 
producing  other  kinds.  We  have  learned  how  to  distin- 
guish chemical  action  from  other  kinds  of  action,  the  loss 
of  their  own  properties  which  the  substances  suffer  being 
a  prominent  characteristic  of  chemical  action. 

How  to  Study  Chemistry. — We  might  learn  a  great  deal 
about  the  facts  of  chemistry  and  learn  very  little  in  regard 
to  the  science  of  chemistry.  As  long  as  we  do  not  recog- 
nize any  connection  between  any  set  of  facts  observed,  or 
as  long  as  only  a  few  connections  are  recognized,  we  cannot 
properly  speak  of  a  subject  as  a  science.  The  subject 
must  have  been  studied  for  a  long  time.  The  laws  govern- 
ing some  of  the  phenomena  of  the  subject  must  have  been 
discovered  before  that  subject  can  be  regarded  as  a  science. 
Before  we  can  have  any  conception  of  the  science  of 
chemistry  we  must  become  acquainted  with  some  of  the 
most  important  facts  of  the  science,  and  we  must  also 
learn  what  connection  exists  between  these  facts.  We 
must  become  familiar  with  substances  as  they  are,  but 
especially  with  the  way  they  act  upon  one  another.  Un- 
fortunately for  our  purpose,  but  very  few  simple  substances 
or  elements  occur  in  the  uncombined  form  in  nature. 


i8  INTRODUCTION    TO   CHEMISTRY. 

While,  therefore,  the  simplest  way  to  begin  the  study  of 
chemical  substances  and  chemical  changes  is  by  an  exam- 
ination of  the  elements,  the  subject  is  complicated  by  the 
fact  that  these  elements  cannot  readily  be  obtained  without 
the  aid  of  substances  which  have  not  been  studied  and  of 
processes  which  it  is  difficult  to  understand  without  some 
knowledge  of  chemistry.  There  are,  however,  two  ele- 
ments that  occur  in  nature  in  enormous  quantities  and 
that  can  be  obtained  in  the  uncombined  condition  very 
easily.  As  the  kinds  of  action  which  these  exhibit  are  of 
great  importance  and  give  an  insight  into  the  nature  of 
chemical  action  in  general,  the  study  of  chemical  phenom- 
ena may  be  profitably  begun  by  the  study  of  these  two 
elements.  They  are  oxygen  and  hydrogen.  In  learning 
the  main  facts  in  regard  to  these  elements  much  will  be 
learned  that  will  be  of  service  in  making  other  chemical 
phenomena  comprehensible. 

The  Elements  and  their  Symbols. — Before  beginning 
this  study  a  list  of  the  elementary  substances  thus  far  dis- 
covered is  here  given.  The  names  of  those  which  are  most 
widely  distributed,  and  which  form  by  far  the  largest  part 
of  the  earth,  are  printed  in  small  capitals.  The  names  of 
those  which  are  very  rare  are  printed  in  italics.  As  has 
been  stated,  not  more  than  a  dozen  elements  enter  largely 
into  the  composition  of  the  earth.  It  has  been  calculated 
that  the  solid  crust  of  the  earth  is  made  up  approximately 
as  represented  in  the  subjoined  table: 


Oxygen 47.29$ 

Silicon. 27.21$ 

Aluminium 7.81$ 

Iron 5.46$ 


Calcium 3. 77 

Magnesium 2.68$ 

Sodium , 2.36$ 

Potassium..  .  2.40$ 


While  oxygen  forms  a  large  proportion  of  the  solid  crust 
of   the   earth,   it  forms   a  still   larger  proportion  (eight 


THE  ELEMENTS  AND   THEIR  SYMBOLS.  19 

ninths)  of  water  by  weight,  and  about  one  fifth  of  the  air 
by  volume.  Carbon  is  the  principal  element  entering  into 
the  structure  of  living  things,  while  hydrogen,  oxygen,  and 
nitrogen  are  also  essential  constituents  of  animals  and 
plants.  Nitrogen  forms  about  four  fifths  of  the  air  by 
volume. 

In  representing  the  results  of  chemical  action  it  is  con- 
venient to  use  abbreviations  for  the  names  of  elements  and 
compounds.  Thus,  instead  of  oxygen  we  may  write  simply 
0,  for  hydrogen  H,  for  nitrogen  N,  etc.  These  symbols 
are  used  in  representing  what  takes  place  when  substances 
act  upon  one  another,  as  will  be  shown  more  clearly  here- 
after. Frequently  the  first  letter  of  the  name  of  the 
element  is  used  as  the  symbol.  If  the  names  of  two  or 
more  elements  begin  with  the  same  letter,  this  letter  is 
used,  but  some  other  letter  of  the  name  is  added.  Thus, 
B  is  the  symbol  of  boron,  Ba  of  barium,  Bi  of  bismuth, 
etc.  In  some  cases  the  symbols  are  derived  from  the  Latin 
names  of  the  elements.  Thus,  the  symbol  for  iron  is  Fe, 
from  Latin  ferrum  ;  for  copper,  Cu,  from  cuprum ;  for 
mercury,  Hg,  from  hydrargyrum,  etc.  The  symbols  of 
the  more  common  elements  will  soon  become  familiar  by 
use.  It  is  not  desirable  to  attempt  to  commit  them  to 
memory  at  this  stage. 

The  names  themselves  are  derived  from  a  variety  of  cir- 
cumstances. Chlorine  is  derived  from  jAcypoS",  which 
means  yellowish  green,  as  this  is  the  color  of  chlorine. 
Bromine  comes  from  /?po3//o?,  a  stench,  a  prominent 
characteristic  of  bromine  being  its  bad  odor.  Hydrogen 
comes  from  vdoop,  water,  and  yeveiv,  to  produce,  signify- 
ing that  it  is  a  constituent  of  water.  Similarly  nitrogen 
comes  from  virpov,  nitre,  and  yereir,  to  produce,  nitro- 
gen being  one  of  the  constituents  of  nitre.  Potassium  is 
an  element  found  in  potash,  and  sodium  is  found  in  soda. 


20 


INTRODUCTION    TO   CHEMISTRY. 


LIST 
ALUMINIUM 

OF  THE  ELEMENTS  AND 
.  Al    HYDROGEN  

THEIl 

...H 

*  SYMBOLS. 

Ruthenium...  . 
Samarium.   .  . 
Scandium  

..Ru 
.  Sa 
...Sc 

Antimony. 

.  .  ..So' 

Indium  

.  In 
.    .1 
.  .  .  Ir 

Argon 

A 

Iodine  
Iridium 

Barium  *  ^* 

Selenium  

Se 

IRON 

SILICON.   .    .  . 

.  .  Si 

Bismuth'.  

Bi 

"Krypton  
Lanthanum.  .  .  . 
Lead  

.   Kr 
,  .'La 
.  Pb 

Silver  

Boron  i  • 

B 

SODIUM  

..Na 

Bromjne.'. 
Cadmium.../.  . 

.,.BP 

"  '  Cs 

Strontium  
Sulphur  
Tantalum  

...Sr 
S 
.  ..Ta 

Lithium 

.  ..Li 
'.'.Mn 

MAGNESIUM  
Manganese.. 

CALCIUM,   .  .    . 
CARBON 

c 

Tellurium.  .  .  . 
Thallium  

.  ..Te 
...Tl 
Th 

Mercury  .  '  
Molybdenum.  .  . 
/Neodymiiim.  .  . 

Neon 

••Hg 
..Mo 

Ne 

Cerium.'. 
CHLORINE  .  *  .  . 
Ckrojnium.:  .  . 
Cobalt  
C/oluiJibium 

..  Co 
Cb' 

Thulium 

Tu 

Tin 

..Sn 

Nickel 

Ni 

..  Ti 

NITROGEN 

N 

Tungsten  

...W 

TI 

Conner  .  . 

...Cu 

LOsmium  
^OXYGEN  
^Palladium  
'Phosphorus...  . 
Platinum 

..Os 
...O 
..Pd 
..   P 
Pt 

Uranium  

^  i~r 
.Erbium 

.E 

>  Vanadium  

.  ...V 

Fluorine;  

(Jaltibtin  
Germanium..  . 
Glucinum  
Gold 

..F 
...<3RT 

.  .  .Ga 
...Ge 
..  .Gl 
Au 

Xenon*.  .".'... 
Ytterbium  
Yttrium  ... 

...X 
...Yt 
.  .».  .Y 

POTASSIUM 

K 

Zinc       .... 

.  .Zri 

•rPraseod'i/m  ium 
'Rhodium  .,-.... 

Rubidium.  . 

.  ..Pr! 
..Rh 
..Kb 

Zirconium  

...Zr 

Helium.  . 

.  He 

CHAPTER   II. 
A   STUDY   OF  THE    ELEMENT   OXYGEN. 

IN  Experiment  4  it  was  shown  that  when  an  electric 
current  is  passed  through  water  containing  sulphuric  acid 
two  gases  are  liberated.  One  of  these  is  distinguished 
by  the  readiness  with  which  substances  burn  in  it.  This 
gas  is  oxygen.  A  gas  with  similar  properties  was  also 
obtained  by  heating  the  red  oxide  of  mercury.  This  is, 
in  fact,  the  same  substance. 

Occurrence  of  Oxygen. — Oxygen  is  the  most  widely  dis- 
tributed element,  and  it  occurs  also  in  very  large  quantity. 
jt  has  been  stated  that  it  forms  nearly  fifty  per  cent  of  the 
solid  crust  of  the  earth,  eight  ninths  of  water,  and  about 
one  fifth  of  the  air. 

Preparation  of  Oxygen. — The  simplest  way  to  obtain 
oxygen  is  by  heating  certain  substances  that  contain  it. 
The  simplest  example  of  this  kind  is  that  furnished  by  the 
oxide  of  mercury,  which  when  heated  yields  mercury  and 
oxygen.  If  the  oxide  is  weighed,  and,  after  decomposi- 
tion, the  oxygen  and  the  mercury  are  weighed,  the  weight 
of  the  mercury  plus  the  weight  of  the  oxygen  will  be  found 
to  be  equal  to  the  weight  of  the  oxide.  Therefore  the 
oxide  contains  only  mercury  and  oxygen.  They  are 
chemically  combined.  When  the  temperature  is  raised 
sufficiently  the  compound  is  resolved  into  its  elements. 
The  chemical  compound  which  contains  mercury  and 

21 


22  INTRODUCTION   TO   CHEMISTRY. 

+ 

oxygen  is  represented  by  writing  the  symbols  of  the  two 
elements  side  by  side,  thus,  HgO,  which  signifies  primarily 
that  the  two  elements  are  in  chemical  combination.  To 
represent  what  takes  place  when  the  oxide  is  heated  this 
equation  is  used  : 

Hg+  0; 


which  is  read,  mercuric  oxide  gives  mercury  and  oxygen. 

Preparation   of    Oxygen   from    Potassium   Chlorate.— 

Another  substance  that  readily  gives  up  oxygen  when 
heated  is  potassium  chlorate.  This  is  a  white,  crystallized 
substance  which  is  manufactured  in  large  quantity  and  is 
sold  at  a  low  price.  It  contains  the  elements  chlorine, 
oxygen,  and  potassium.  When  heated  to  a  sufficiently 
high  temperature  it  gives  off  all  its  oxygen,  a  compound 
of  potassium  and  chlorine  being  left  behind.  The  chemi- 
cal changes  brought  about  in  potassium  chlorate  by  heat- 
ing it  are  interesting,  and  tliey  will  be  studied  somewhat 
in  detail  a  little  later.  At  present  they  are  of  interest 
mainly  because  they  furnish  the  element  oxygen. 

EXPERIMENT  16.  —  Arrange  an  apparatus  as  shown  in  Fig.  7. 
A  represents  a  retort  of  about  100  com.  capacity.  B  is  a  piece  of 
rubber  tubing  which  is  in  turn  connected  with  a  piece  of  glass 
tubing  bent  upward  at  the  end.  This  end  is  placed  under  the 
surface  of  the  water  in  C.  In  A  put  2  to  3  grams  (about  a  six- 
teenth of  an  ounce)  potassium  chlorate,  and  gently  heat  by  means 
of  «the  lamp.  Notice  carefully  what  takes  place.  At  first  the 
potassium  chlorate  will  melt,  forming  a  clear  liquid.  If  the  heat 
is  increased,  the  liquid  will  appear  to  boil,  and  it  will  soon  be  seen 
that  a  gas  is  being  given  oil  Now  bring  the  inverted  cylinder  E 
filled  with  water  over  the  end  D  of  the  tube,  and  let  the  bubbles 
of  gas  rise  in  the  cylinder.  After  a  considerable  quantity  of  gas 
has  been  collected  in  this  way  the  action  stops,  the  mass  in  the 
flask  becomes  solid,  and  apparently  the  end  of  the  process  is 
reached.  But  if  the  heat  is  raised  still  higher,  gas  will  again 
come  off,  and  in  this  second  stage  a  larger  quantity  will  be  col- 


OXYGEN  FROM  MANGANESE  DIOXIDE. 


23 


lected  than  in  the  first.  Finally,  however,  the  end  is  reached, 
and  the  substance  left  in  the  flask  remains  unchanged,  no  matter 
how  long  heat  may  be  applied.  Examine  the  gas  as  in  Experi- 
ments 3  and  4.  It  will  be  shown  later  that  in  the  first  stage  of 
the  decomposition  of  potassium  chlorate  the  products  are  potas- 
sium pet-chlorate  and  oxygen,  and  that  in  the  second  stage  the 
potassium  perchlorate  is  decomposed  into  potassium  chloride  and 
oxygen,  so  that  the  final  products  of  the  action  are  potassium 
chloride  and  oxygen. 


FIG.  7. 

Oxygen  from  Manganese  Dioxide.  —  Another  good 
method  for  preparing  oxygen  consists  in  heating  black 
oxide  of  manganevse.  This  is  a  compound  found  in  nature, 
called  by  mineralogists  pyrolusite,  and  by  chemists  man- 
ganese dioxide.  It  consists  of  the  elements  manganese 
and  oxygen.  When  this  substance  is  heated  it  loses  part 
of  its  oxygen,  and  there  is  left  behind  another  compound 
of  manganese  and  oxygen  containing  the  elements  in 
different  proportions. 

EXPERIMENT  17. — Make  oxygen  by  heating  to  redness  4  to  5 
grams  (about  an  eighth  of  an  ounce)  of  manganese  dioxide  in  a 
hard-glass  tube  closed  at  one  end  and  connected  at  the  other  end 
by  means  of  a  cork  with  a  bent  glass  tube. 

Oxygen  from  Potassium  Chlorate  and  Manganese  Di- 
oxide.— The  most  convenient  way  to  make  oxygen  in  the 


24  INTRODUCTION    TO   CHEMISTRY. 

laboratory  is  to  heat  a  mixture  of  equal  parts  by  weight  of 
potassium  chlorate  and  manganese  dioxide.  This  mixture 
gives  off  oxygen  readily  when  heated.  The  potassium 
chlorate  gives  up  its  oxygen  under  these  circumstances. 
The  manganese  dioxide  takes  part  in  the  decomposition, 
but  remains  behind  finally  in  its  original  form.  The 
chemical  changes  involved  are  quite  complicated  and 
cannot  be  studied  profitably  at  this  stage. 

EXPERIMENT  18. — Mix  25  to  30  grams  (or  about  an  ounce;  of 
coarsely  powdered  potassium  chlorate  with  an  equal  weight  of 
coarsely  powdered  manganese  dioxide  in  a  mortar.  The  sub- 


FIG.  8. 


stances  should  not  be  in  the  form  of  powder.  Test  the  mixture 
by  heating  a  small  quantity  of  it  in  a  dry  test-tube.  If  the  decom- 
position takes  place  quietly,  put  the  mixture  in  a  retort,  arranged 
as  shown  in  Fig.  7,  heat  it,  and  collect  the  gas  by  displacement 
of  water  in  appropriate  vessels, — cylinders,  bell-jars,  bottles  with 


PHYSICAL  PRO  PERT  IPS   OF  OXYGEN.  25 

wide  mouths,  etc.  It  will  also  be  well  to  collect  some  in  a  gas- 
ometer, such  as  is  commonly  found  in  chemical  laboratories,  the 
essential  features  of  which  are  represented  in  Fig.  8.  It  is  made 
either  of  metal  or  of  glass.  The  opening  at  d  can  be  closed  by 
means  of  a  screw-cap.  In  order  to  fill  it  with  water  open  the  stop- 
cocks and  pour  the  water  into  the  upper  part  of  the  vessel  after 
lidvi  ug  screwed  the  cap  on  to  d.  When  it  is  full,  water  will  flow  out 
of  the  small  tube  e.  Now  close  all  the  stop-cocks,  and  take  the 
cap  from  d.  The  water  will  stay  in  the  vessel  for  the  same  reason 
that  it  will  stay  in  the  cylinder  inverted  with  its  month  below 
water.  To  fill  the  gasometer  with  gas,  put  it  over  a  tub  or  sink 
and  introduce  the  tube  from  which  gas  is  issuing  into  the  open- 
ing at  d.  The  gas  will  rise  and  displace  the  water,  which  will 
flow  out  at  d.  When  full,  screw  the  cap  on.  To  get  the  gas  out 
of  the  gasometer,  attach  a  rubber  tube  to  e,  pour  water  into  the 
upper  part  of  the  gasometer,  open  the  stop-cock  a  and  that  at  e, 
when  the  gas  will  flow  out,  and  the  current  can  be  regulated  by 
means  of  the  stop-cock  at  e. 

Physical  Properties  of  Oxygen. — In  the  first  place,  the 
gas  is  invisible/  The  slight  cloud  which  appears  in  the 
vessels  when  the  gas  is  first  collected  is  due  to  the  presence 
of  a  small  quantity  of  a  substance  which  is  not  oxygen.  If 
the  vessels  are  allowed  to  stand  for  a  few  minutes  the  cloud 
will  disappear,  and  the  vessels  will  look  the  same  as  if  they 
were  filled  with  air.  The  gas  is  tasteless,  and  inodorous. 

EXPERIMENT  19.— Inhale  a  little  of  the  gas  from  one  of  the 
small  bottles. 

Oxygen  is  slightly  heavier  than  the  air.  This  can  be 
determined  by  weighing  a  globe  filledTwith  air,  then  driv- 
ing out  the  air  by  passing  a  current  of  oxygen  through  it 
for  some  time,  and  weighing  it  again.  If  these  weighings 
are  carefully  made,  it  will  be  found  that  the  relation 
between  the  weights  of  equal  volumes  of  air  and  oxygen  is 
1  :  1.1056.  Or,  in  other  words,  if  a  certain  volume  of 
air  weighs  1  gram,  the  same  volume  of  oxygen  will  weigh 
1.1056  grams.  When  gaseous  oxygen  is  subjected  to  high 
pressure  and  a  temperature  below  —  119°,  it  is  converted 


26  INTRODUCTION   TO   CHEMISTRY. 

into  a  blue  liquid  which  boils  at  —  181°.     (See  LIQUID 
AIR.) 

The  properties  of  oxygen  to  which  reference  has  thus 
far  been  made  are  its     lisicaLjMt  ies      These  are  its 


appearance,  taste,  smell,  relative  weight^  and  changes  in 
its  condition,  which  still  leave  it  in  the  elementary  form 
uncombined  chemically.  Our  knowledge  of  oxygen  must, 
of  course,  include  a  knowledge  of  its  physical  properties, 
but,  from  the  chemical  point  of  view,  it  is  more  important 
for  us  to  know  how  oxygen  acts  chemically.  What  chemi- 
cal changes  is  it  capable  of  bringing  about  ?  What  condi- 
tions are  necessary  in  order  that  it  may  act  chemically  ? 
What  laws  govern  the  action  ?  What  products  are  formed  ? 

Chemical  Conduct  of  Oxygen.  —  In  order  to  learn  how 
oxygen  acts  upon  some  simple  substances  under  ordinary 
circumstances,  we  may  perform  a  few  experiments. 

EXPERIMENT  20.—  Turn  three  of  the  bottles  containing  oxygen 
with  the  mouth  upward,  leaving  them  covered  with  glass  plates. 
Into  one  introduce  some  sulphur  in  a  so-called  deflagrating-spoon, 
which  is  a  small  cup  of  iron  or  brass  attached  to  a  stout  wire 
which  passes  through  a  round  metal  plate,  usually  of  tin.  (See 
Fig.  9.)  In  another  put  a  little  charcoal  (carbon),  and  Hi  a  third 
a  piece  of  phosphorus  *  about  the  size  of  a  pea.  Let  them  stand 
quietly  and  notice  what  changes,  if  any,  take  place.  Sulphur, 
carbon,  and  phosphorus  are  elements,  and  oxygen  is  an  element. 
It  will  be  noticed  that  the  sulphur  and  the  carbon  remain  un- 
changed, while  some  change  takes  place  in  the  phosphorus,  as  is 
shown  by  the  appearance  of  white  fumes  in  the  vessel  containing 
it.  After  some  time  the  phosphorus  will  disappear  entirely,  the 
fumes  will  also  disappear,  and  there  will  be  nothing  visible  to 

*  Phosphorus  should  be  handled  with  great  care.  It  is  always 
kept  under  water,  usually  in  the  form  of  sticks.  If  a  small  piece  is 
wanted,  take  out  a  stick  with  a  pair  of  forceps,  and  put  it  under 
water  in  an  evaporating-  dish.  While  it  is  under  the  water,  cut  off  a 
piece  of  the  size  wanted.  Take  this  out  by  means  of  a  pair  of  forceps, 
lay  it  for  a  moment  on  a  piece  of  filter-paper,  which  will  absorb  most 
of  the  water,  then  quickly  put  it  in  the  spoon. 


CHEMICAL    CONDUCT  OF  OXYGEN.  27 

show  us  what  has  become  of  the  phosphorus.  If  the  temperature 
of  the  room  is  rather  high,  it  may  happen  that  the  phosphorus 
will  take  fire.  If  it  should,  it  will  burn  with  an  intensely  bright 
light.  After  the  burning  has  stopped,  the  vessel  will  be  filled 
with  white  fumes,  but  these  will  soon  disappear,  and  the  vessel 
will  apparently  be  empty. 

What  these  Experiments  Show.  —  These  experiments 
show  that  oxygen  does  not  act  upon  sulphur  and  carbon 
when  brought  in  contact  with  them  at  the  ordinary  tem- 
perature, and  that  the  action  upon  phosphorus  is  generally 
slight.  We  might  perform  experiments  of  this  kind  with 
a  great  many  substances,  and  we  should  reach  the  conclu- 
sion that  at  ordinary  temperatures  oxygen  does  not  act 
upon  most  substances. 

Action  of  ixygen  at  Higher  Temperatures, — If,  how- 
ever, the  substances  are  heated  before  they  are  introduced 
into  the  oxygen,  the  results  will  be  entirely  different. 
Instead  of  conducting  itself  as  an  inactive  element,  oxygen 
will  act  with  great  ease  upon  many  substances.  Things 
such  as  coal,  wood,  etc.,  which  we  know  will  burn  in  the 
air,  burn  in  oxygen  much  more  readily,  and  several  sub- 
stances such  as  iron,  copper,  etc.,  which  will  not  burn  in 
the  air,  burn  in  oxygen  with  ease. 

EXPERIMENT  21.— In  a  deflagrating-spoon  set  fire  to  a  little 
sulphur  and  let.  it  burn  in  the  air. 
Notice  wrhether  it  burns  with  ease  or 
with  difficulty.  Notice  the  odor  of  the 
fumes  W7hich  are  given  off.  Now  set 
fire  to  another  small  portion  and  intro- 
duce it  in  a  spoon  into  one  of  the  ves- 
sels containing  oxygen,  as  shown  in 
Fig.  9.  It  will  be  seen  that  the  sulphur 
burns  much  more  readily  in  the  oxy- 
gen than  in  the  air.  Notice  the  odor 
of  the  fumes  given  off.  Is  it  the  same 
as  that  noticed  when  the  burning  takes 
place  iii  the  air  ? 


28  INTRODUCTION    TO   CHEMISTRY. 

FIxPERiMENT  22. — Perform  similar  experiments  with  charcoal. 

EXPERIMENT  23. — Burn  a  piece  of  phosphorus  not  larger  than 
a  small  pea  in  the  air  and  in  oxygen.  In  the  latter  case  the  light 
emitted  from  the  burning  phosphorus  is  so  intense  that  it  is  pain- 
ful to  some  eyes  to  look  at  it.  It  is  better  to  be  cautious.  The 
phenomenon  is  an  extremely  brilliant  one.  The  walls  of  the 
vessel  in  which  the  burning  takes  place  become  covered  with  a 
white  substance  which  afterwards  gradually  disappears. 

EXPERIMENT  24. — Straighten  a  steel  watch-spring  *  and  fasten 
it  in  a  piece  of  metal,  sucli  as  is  used  for  fixing  a  deflagrating- 
spoon  in  an  upright  position  ;  wind  a  little  thread  around  the 
lower  end,  and  dip  it  in  melted  sulphur.  Set  fire  to  this  and  in- 
sert it  into  a  vessel  containing  oxygen.  For  a  moment  the  sul- 
phur will  burn  as  in  Experiment  21  ;  but  soon  the  steel  begins  to 
burn  brilliantly,  and  the  burning  continues  as  long  as  there  is 
oxygen  left  in  the  vessel.  Notice  that  in  this  case  there  is  no 
flame,  but  instead  very  hot  particles  are  given  off  from  the  burn- 
ing iron.  The  phenomenon  is  of  great  beauty,  especially  if  ob- 
served in  a  dark  room.  The  walls  of  the  vessel  become  covered 
with  a  dark  reddish-brown  substance,  some  of  which  will  also  be 
found  at  the  bottom  in  larger  pieces.  This  substance  is  a  com- 
pound of  iron  and  oxygen  known  as  magnetic  oxide  of  iron. 

What  has  Taken  Place  ? — What  has  taken  place  in  these 
experiments  ?  In  the  first  place,  the  substances  were 
simply  heated  before  being  introduced  into  the  oxygen. 
Nothing  was  added  to  them  except  heat.  It  is  clear  that 
while  oxygen  does  not  act  upon  these  substances  at 
ordinary  temperatures,  it  does  act  upon  them  at  higher 
temperatures.  But  what  does  the  action  consist  in  ?  We 
can  determine  this  only  by  a  careful  study  of  the  sub- 
stances before  and  after  the  action.  We  must  know  not 
only  what  substances  are  brought  together,  but  also  what 

*  Old  watch-springs  can  generally  be  had  of  any  watch  maker  or 
mender  for  the  asking.  A  spring  can  be  straightened  by  unrolling 
it,  attaching  a  weight,  and  suspending  the  weight  by  the  spring. 
The  spring  is  then  heated  to  redness  from  one  end  to  the  other  by 
means  of  a  Bunsen  burner. 


CHEMICAL   CONDUCT  OF  OXYGEN.  29 

weight  of  each;  and  we  must  know  what  substances  are  left 
behind,  and  the  exact  weights  of  these.  In  the  cases 
mentioned  it  would  be  a  difficult  matter  for  one  not 
thoroughly  trained  in  the  use  of  chemical  methods  to  make 
all  these  determinations  accurately,  and  unless  they  were 
made  accurately  they  would  fail  to  furnish  the  desired 
explanation.  The  determinations  have  fortunately  been 
made  so  frequently  that  there  can  be  no  doubt  as  to  what 
would  be  found  were  the  experiments  to  be  repeated,  and 
for  the  present  it  will  be  necessary  to  accept  the  results, 
and  use  them  as  the  basis  of  our  reasoning.  Something, 
however,  may  be  learned  with  but  little  difficulty.  If  in 
the  experiment  with  sulphur  the  spoon  is  examined  after 
the  burning  stops,  it  will  be  found  that  the  sulphur  has 
disappeared.  It  will  also  be  noticed  that  there  is  present 
an  invisible  *  substance  which  has  a  strong,  disagreeable 
odor.  This  substance  is  not  oxygen  and  it  is  not  sulphur, 
but  it  is  a  gas  which  is  formed  by  the  burning  of  sulphur 
in  oxygen.  What  has  become  of  the  oxygen  ?  That  it  is 
no  longer  present  in  its  original  condition  may  be  shown 
by  introducing  a  burning  stick  into  the  vessel.  Instead  of 
continuing  to  burn  with  increased  activity,  as  we  have  seen 
it  do  in  oxygen,  it  is  extinguished. 

In  the  experiment  with  carbon  the  results  are  similar, 
only  the  invisible  substance  has  no  odor. 

In  the  experiment  with  phosphorus  the  white  substance 
which  is  deposited  on  the  walls  of  the  vessel  is  not  phos- 
phorus, as  is  clear  from  the  fact  that  it  dissolves  in  water. 

Proof  that  the  Oxygen  Combines  with  the  Burning  Sub- 
stance.— The  oxygen  being  invisible,  it  is  more  difficult  to 
determine  whether  it  enters  into  combination  or  not,  but 
that  it  does  can  be  shown  by  properly  devised  experiments. 

*  The  fumes  first  noticed  subside  if  a  little  water  is  in  the  bottle. 


3° 


INTRODUCTION    TO   CHEMISTRY. 


It  is  only  necessary  to  burn  a  substance  in  a  closed  vessel 
containing  oxygen,  and  to  determine,  after  the  burning, 
whether  there  is  less  oxygen  than  there  was  before. 


FIG.  10. 

Lavoisier,  who  first  showed  what  part  the  oxygen  plays  in 
burning,  made  a  very  important  experiment  much  like  the 
following :  Some  phosphorus  is  enclosed  in  a  sealed  tube 
with  oxygen,  and,  by  heating  from  without,  the  phos- 
phorus is  set  on  fire.  After  the  action  is  over,  one  end  of 
the  tube  is  broken  off  under  water,  when  water  rushes  in, 
showing  that  the  gas  that  was  in  the  tube  has  disappeared. 
A  modification  of  this  experiment  is  here  described. 

EXPERIMENT  25. — Arrange  an  apparatus  as  shown  in  Fig.  10. 
A  is  a  glass  tube  about  60  cm.  (2  feet)  long  and  about  3f  cm.  (1£ 


CHEMICAL  CONDUCT  OF  OXYGEN.        31 

inches)  in  diameter.  This  is  connected  by  means  of  a  bent  tube 
with  the  small  flask  B,  of  50  to  100  ccm.  capacity,  which  is  fitted 
with  a  stopper  having  two  holes.  This  flask  is  carefully  dried, 
and  three  layers  of  thin  asbestos  paper  laid  on  the  bottom  inside, 
and  upon  this  a  thin  layer  of  iron  dust  or  fine  iron  filings.  The 
lower  end  of  A  is  immersed  to  the  extent  of  about  5  cm.  (2  inches) 
in  water.  A  current  of  oxygen  is  now  passed  through  the  appa- 
ratus by  connecting  at  C  with  a  gasometer.  When  the  air  has 
been  displaced  the  current  of  oxygen  is  stopped,  and  the  stop-cock 
at  the  end  of  C  is  closed.  Now  heat  the  flask  gently.  When  the 
iron  begins  to  glow,  remove  the  flame.  What  evidence  is  furnished 
that  the  oxygen  enters  into  combination  and  disappears  as  a  gas  ? 

Products  Formed. — Experiments  of  the  kind  described 
have  shown  that,  whenever  a  substance  burns  in  oxygen, 
both  the  substance  and  the  oxygen  lose  their  characteristic 
properties,  and  that  something  else  is  formed  in  their 
place.  In  other  words,  the  process  is  one  of  chemical 
combination.  Sulphur  combines  with  oxygen  to  form  a 
gaseous  product  known  as  sulphur  dioxide.  It  is  this  gas 
that  gives  the  strong  odor  when  sulphur  burns.  Carbon 
combines  with  oxygen  to  form  the  invisible  gas  carbon 
dioxide,  commonly  called  carbonic  acid  gas.  Phosphorus 
combines  with  oxygen  to  form  a  white  solid,  phosphorus 
pentoxide,  which  dissolves  in  the  water  present  and  dis- 
appears. All  these  products  are  well  known,  and  they  will 
be  studied  when  the  elements  sulphur,  carbon,  and  phos- 
phorus are  taken  up. 

Proportions  by  Weight  in  which  the  Substances  Com- 
bine with  Oxygen. — The  next  question  that  naturally  pre- 
sents itself  is  this:  In  what  proportions  by  weight  do  the 
substances  combine  with  oxygen  ?  Is  there  anything 
definite  in  these  proportions,  or  do  they  combine  in  any 
possible  proportions  ?  This  is  a  very  important  question, 
{iiid  it  has  given  rise  to  a  great  deal  of  experimenting, 
especially  in  the  early  part  of  the  last  century.  It  is  impos- 


32  INTRODUCTION    TO   CHEMISTRY. 

sible  to  repeat  these  experiments  here,  but  the  method  of 
work  can  be  made  clear  by  a  general  account.  Suppose 
magnesium  is  taken  for  experiment,  A  small  quantity  is 
accurately  weighed  by  a  chemical  balance.  It  is  now 
heated  in  oxygen,  and,  after  the  action  is  complete,  the 
product  is  weighed.  The  experiment  is  repeated  a  num- 
ber of  times,  and  all  the  weights  arc  carefully  recorded. 
If  every  precaution  is  taken  to  secure  accuracy,  it  will  be 
found  that  these  elements  dlivays  combine  in  the  same  pro- 
portion by  weight :  1  gram  of  oxygen  combines  with  1^ 
grams  of  magnesium.  By  similar  experiments  it  has  been 
shown  that  whenever  carbon  burns  in  oxygen  these  two 
elements  combine  in  the  same  proportion  by  weight — 
I  gram  of  carbon  combining  with  2|  grams  of  oxygen ;  and 
similar  results  have  been  obtained  in  all  other  cases.  This 
act  of  combining  with  oxygen  is  one  involving  the  action 
of  definite  weights  of  substances. 

Relation  of  the  Weight  of  the  Product  to  the  Weights 
of  the  Combining  Substances. — In  the  experiment  with 
magnesium  described  in  the  preceding  paragraph  the 
oxygen  was  not  weighed.  The  increase  in  the  weight  of 
the  magnesium  caused  by  combination  with  oxygen  was 
determined,  and  the  increase  was  ascribed  to  oxygen.  A 
thoroughly  satisfactory  experiment  would,  however,  in- 
volve the  weighing  of  the  magnesium,  of  the  oxygen,  and 
oi  the  product  formed.  Such  experiments  have  been 
made  in  great  number,  and  it  has  been  shown  that  the 
weight  of  the  substance  burned  plus  that  of  the  oxygen 
used  up  is  exactly  equal  to  the  weight  of  the  substance 
formed. 

Burning  in  the  Air, — One  cannot  well  help  noticing  a 
strong  resemblance  between  the  burning  of  substances  in 
oxygen  and  in  the  air,  and  the  question  naturally  suggests 


COMBUSTION -KINDLING    TEMPERATURE.  33 

itself,  'Are  these  two  acts  the  same  ?  The  only  way  to 
answer  this  question  is  to  burn  the  same  things  in.  pure 
oxygen  and  in  air,  and  to  see  whether  the  same  product 
is  formed  in  each  case,  and  whether  anything  else  is 
formed.  If  this  comparison  should  be  made  in  any  case 
it  would  be  found  that  whether  a  substance  burns  in  the 
air  or  in  pure  oxygen  the  same  product  is  formed,  and 
nothing  else.  It  is  therefore  certain  that  the  act  of  burn- 
ing in  the  air  is  due  to  the  presence  of  oxygen.  We  shall 
learn  later  that  the  reason  why  substances  do  not  burn  as 
readily  in  the  air  as  in  pure  oxygen  is  that  in  the  air  there 
is  present  a  large  quantity  of  another  gas  wrhich  does  not 
act  upon  the  substances  at  all. 

Combustion. — By  the  term  combustion  in  its  broadest 
sense  is  meant  any  chemical  act  that  is  accompanied  by  an 
evolution  of  light  and  heat.  Ordinarily,  however,  it  is 
restricted  to  the  union  of  substances  with  oxygen  as  this 
union  takes  place  in  the  air,  with  evolution  of  light  and 
heat.  Substances  which  have  the  power  to  unite  with 
oxygen  are  said  to  be  combustible,  and  substances  which 
have  not  this  power  are  said  to  be  incombustible.  Most 
elements  combine  with  oxygen  under  proper  conditions, 
and  are  therefore  combustible.  Most  compounds  formed 
by  the  union  of  oxygen  with  combustible  substances  are 
incombustible.  For  example,  the  carbon  dioxide  and 
phosphorus  pentoxide  obtained  in  Experiments  22  and  23 
are  incombustible.  They  contain  oxygen,  and  they  canno 
directly  combine  with  any  more. 

Kindling  Temperature. — We  have  seen  that  substances 
do  not  usually  combine  with  oxygen  at  ordinary  tempera- 
tures, but  that  in  order  to  effect  the  union  the  temperature 
must  be  raised.  If  this  were  not  the  case,  it  is  plain  that 
every  combustible  substance  in  nature  would  burn  up,  for 


34  INTRODUCTION    TO   CHEMISTRY. 

the  air  supplies  a  sufficient  quantity  of  oxygen  for  this 
purpose.  Some  substances  need  to  be  heated  to  <r  high 
temperature  before  they  will  combine  witR  oxygen  Bothers 
require  but  very  slight  elevation.  If  we  were  to  subject  a 
piece  of  phosphorus,  of  sulphur,  and  of  carbon  to  the  same 
gradual  rise  in  temperature,  we  should  find  that  the  phos- 
phorus takes  fire  very  easily,  only  a  slight  elevation  of 
temperature  being  necessary;  next  in  order  would  come 
the  sulphur;  and  last  the  carbon.  If  we  were  to  repeat 
these  experiments  a  number  of  times,  we  should  find  that 
the  phosphorus  would  always  take  fire  at  the  same  tem- 
perature, and  a  similar  result  would  be  reached  in  the 
case  of  sulphur  and  carbon.  Every  combustible  sub- 
stance has  its  kindling  temperature ;  that  is,  the  tempera- 
ture at  which  it  will  unite  with  free  oxygen.  Below  this 
temperature  it  will  not  unite  with  oxygen  except  very 
slowly.  If  a  piece  of  wood  could  be  heated  to  its  kindling 
temperature  all  at  once,  it  would  burn  up  as  rapidly  as  it 
could  secure  the  necessary  oxygen;  but  the  burning  does 
not  usually  take  place  rapidly,  for  the  reason  that  only  a 
small  part  of  it  is  at  any  one  time  heated  to  the  kindling 
temperature.  Watch  a  stick  of  wood  burning,  and  see 
how,  as  we  sa}%  "the  fire  creeps"  slowly  along  it.  The 
reason  of  the  slow  advance  is  simply  this :  only  those  parts 
of  the  stick  that  are  nearest  the  burning  part  become 
heated  to  the  kindling  temperature. 

Slow  Oxidation. — Substances  may  combine  slowly  with 
oxygen  without  evolution  of  light.  Thus,  if  a  piece  of  iron 
is  allowed  to  lie  in  moist  air,  it  becomes  covered  with  rust. 
This  rust  is  similar  to  the  substance  formed  when  iron  is 
burned  in  oxygen.  Both  are  formed  by  the  union  of  iron 
and  oxygen.  Magnesium  burns  in  the  air,  as  we  have 
seen,  and  forms  a  white  compound  containing  oxygen.  It 
burns  with  increased  brilliancy  in  oxygen,  forming  the 


BREATHING— HEAT   OF  COMBUSTION.  35 

same  compound.  If  left  in  moist  air  for  some  days  or 
weeks,  it  becomes  covered  with  a  layer  of  the  same  white 
substance.  If  this  is  scraped  off  and  the  magnesium  is 
further  exposed,  it  will  again  become  covered  with  a  layer 
of  the  compound  with  oxygen,  and  this  may  be  continued 
until  the  magnesium  has  been  completely  converted  into 
the  same  substance  that  is  formed  when  it  burns  in  oxygen 
or  in  the  air.  Many  other  similar  cases  of  slow  oxidation 
might  be  described,  some  of  which,  such  as  the  decay  of 
wood,  are  constantly  taking  place  in  nature. 

Breathing. — The  most  important  illustration  of  slow 
oxidation  is  that  which  takes  place  in  our  bodies,  for,  as 
we  shall  see,  the  food  which  we  partake  of  undergoes  a 
great  many  changes;  some  of  the  substances  uniting  with 
oxygen,  and  thus  keeping  up  the  temperature  of  our 
bodies.  This,  however,  is  done  without  evolution  of  light 
and  without  marked  evolution  of  heat.  We  take  large 
quantities  of  oxygen  into  our  lungs  in  breathing.  This 
acts  upon  various  substances  presented  to  it,  oxidizing 
them  to  other  forms  which  can  easily  be  got  rid  of.  More 
will  be  said  in  regard  to  the  breathing  process  of  animals 
and  plants  when  the  subject  of  carbon  and  its  compounds 
with  oxygen  is  considered. 

Heat  of  Conftmstion. — What  is  the  chief  difference  be- 
tween combustion,  as  we  ordinarily  understand  it,  and  slow 
oxidation  ?  So  far  as  we  can  judge  by  a  cursory  examina- 
tion, it  is  that  in  the  former  light  and  heat  are  produced, 
while  in  the  latter  no  light  and  very  little  or  no  heat  is 
produced.  Remembering  that  the  reason  why  a  body  gives 
light  is  that  it  is  heated  to  a  sufficiently  high  temperature, 
the  problem  resolves  itself  into  a  question  of  heat.  What 
difference,  if  any,  is  there  between  the  quantity  of  heat 
given  off  when  a  substance  burns  and  when  it  undergoes 


36  INTRODUCTION   TO   CHEMISTRY. 

slow  oxidation  without  evolution  of  light  ?  The  answer  is 
of  the  highest  importance.  There  is  no  difference  what- 
ever. In  the  one  case  the  heat  is  all  given  oil  in  a  short 
space  of  time,  and  therefore  the  temperature  of  the  sub- 
stance becomes  high  and  it  emits  light.  In  the  other  the 
heat  is  evolved  slowly  and  continues  for  a  much  longer 
time,  and  therefore  the  temperature  of  the  substance  does 
not  get  very  high,  as  surrounding  substances  conduct  off 
the  heat  as  rapidly  as  it  is  evolved.  If,  however,  we  were 
to  measure  the  quantity  of  the  heat,  we  should  find  it  to 
be  the  same  in  both  cases. 

How  the  Quantity  of  Heat  is  Measured. — The  quantity 
of  heat  given  off  in  a  chemical  reaction  can  be  measured 
by  allowing  the  reaction  to  take  place  in  a  vessel  called  a 
calorimeter,  so  constructed  as  to  prevent  loss  of  heat,  and 
containing  a  known  weight  of  water.  The  temperature  of 
the  water  is  noted  at  the  beginning  of  the  operation  and  at 
the  end.  A  quantity  of  heat  is  generally  stated  by  giving 
the  number  of  grams  of  water  which  it  will  raise  one 
degree  (Centigrade)  in  temperature.  The  quantity  of  heat 
necessary  to  raise  the  temperature  of  a  gram  of  water  from 
0°  to  1°  (Centigrade)  is  the  unit  used  in  heat-measurement. . 
It  is  called  the  calorie.  If,  therefore,  we  say  the  quantity 
of  heat  evolved  in  any  reaction  is  250  calories  (written 
generally  250  cal.),  we  mean  simply  a  quantity  of  heat 
which  would  raise  the  temperature  of  250  grams  of  water 
one  degree  (Centigrade)  in  temperature.  . 

To  repeat,  then:  By  the  heat  of  combustion  of  a  sub- 
stance is  meant  the  quantity  of  heat  given  off  when  a 
certain  weight  of  the  substance  combines  with  oxygen. 

It  will  be  found  that  not  only  is  the  heat  of  combustion 
a  fixed  quantity  whether  the  union  with  oxygen  takes  place 
slowly  or  rapidly,  but  that  the  heat  evolved  in  any  given 
chemical  reaction  is  always  the  same,  and  that  chemical 


CHEMICAL  ENERGY  AND  CHEMICAL  WORK.    37 

combination  is  always  accompanied  by  an   evolution   of 
heat. 

Heat  of  Decomposition. — Just  as  it  is  true  that  a  definite 
quantity  of  heat  is  evolved  when  two  or  more  element,8 
combine  chemically,  so  also  it  is  true  that  in  order  to 
decompose  the  compound  formed  the  same  quantity  of 
heat  is  required. 

Chemical  Energy  and  Chemical  Work. — Any  substance 
that  has  the  power  to  unite  with  others  can  do  chemical 
work, — it  possesses  chemical  energy.  Thus,  all  combusti- 
ble substances  can  do  work.  In  uniting  with  oxygen  heat 
is  evolved,  and  this  can  be  transformed  into  motion.  To 
go  back  to  the  example  of  the  steam-engine,  the  cause  of 
the  motion  is  the  burning  of  the  fuel.  It  will  thus  be  seen 
that  the  source  of  the  power  in  the  steam-engine  is  chemi- 
cal energy.  Substances  that  have  not  the  power  to  com- 
bine with  others  have  no  power  to  do  chemical  work,  or 
they  have  no  chemical  energy.  As  far  as  power  to  com- 
bine with  oxygen  is  concerned,  water  is  a  substance  of  this 
kind,  as  is  also  carbon  dioxide,  the  gas  formed  when 
carbon  is  burned  in  oxygen.  In  order  that  they  may  do 
work,  they  must  first  be  decomposed  and  their  constituents 
put  together  in  some  form  in  which  they  have  the  power 
of  combination.  This  decomposition  of  carbon  dioxide 
and  water  is  taking  place  constantly  on  the  earth.  All 
plant-life  is  dependent  on  it.  The  products  of  the  action, 
as,  for  example,  the  different  kinds  of  wood,  have  energy, 
— they  can  do  chemical  work.  This  power  to  do  work  has 
been  acquired  from  the  heat  of  the  sun,  to  which  the 
decomposition  of  the  carbon  dioxide  and  water  is  mainly 
due.  There  is  thus  a  transformation  of  the  sun's  heat  into 
chemical  energy,  which  is  stored  up  in  the  combustible 
wood.  The  quantity  of  heat  that  would  be  given  oft'  in 


38  INTRODUCTION   TO  CHEMISTRY. 

burning  the  wood  is  exactly  equal  to  the  quantity  used  up 
in  its  formation. 

Oxides. — The  compounds  of  oxygen  with  other  elements 
are  called  oxides.  To  distinguish  between  different  oxides 
the  name  of  the  element  with  which  the  oxygen  is  in  com- 
bination is  prefixed.  Thus  the  compound  of  zinc  and 
oxygen  is  called  zinc  oxide;  that  of  calcium  and  oxygen, 
calcium  oxide;  that  of  silver  and  oxygen,  silver  oxide,  etc. 


CHAPTER  III. 
HYDROGEN. 

IN"  Experiment  4  it  was  found  that  when  an  electric  cur- 
rent is  passed  through  water  two  gases  are  obtained,  one 
of  which  has  since  been  studied  and  found  to  be  oxygen. 
The  other,  it  will  be  remembered,,  takes  fire  and  burns, 
and  is  thus  easily  distinguished  from  oxygen.  This  second 
gas  is  hydrogen. 

Occurrence. — Hydrogen  is  found  in  nature  very  widely 
distributed,  and  in  large  quantity.  It  forms  one  ninth  of 
the  weight  of  water,  and  is  contained  in  all  substances  that 
enter  into  the  composition  of  plants  and  animals. 

Preparation  of  Hydrogen. — It  can  be  prepared : 

(a)  By  decomposition  of  water  by  means  of  the  electric 
current ; 

(b)  By  decomposition  of  water  by  the  action  of  certain 
metals ; 

(c)  By   the   action   of   substances  known   as   acids   on 
metals. 

The  following  experiments  will  illustrate  these  methods. 

EXPERIMENT  26.— Repeat  Experiment  4  and  examine  the  gases. 
EXPERIMENT  27. — Throw  a  small  piece  of  sodium  *  on  water. 

*  The  metals  sodium  and  potassium  are  kept  under  oil.  When  a 
small  piece  is  wanted  take  out  one  of  the  larger  pieces  from  the 
bottle,  roughly  wipe  off.  the  oil  with  filter-paper  and  cut  off  a  piece 
the  size  needed.  It  is  not  advisable  to  use  a  piece  larger  than  an 
ordinary  pea. 

39 


40  INTRODUCTION   TO   CHEMISTRY. 

While  it  is  floating  on  the  surface  apply  a  lighted  match  to  it. 
A  yellow  flame  will  appear.  This  is  burning  hydrogen,  the  flame 
being  colored  yellow  by  the  presence  of  the  sodium,  some  of 
which  also  burns.  Make  the  same  experiment  with  potassium. 
The  flame  appears  in  this  case  without  the  aid  of  the  match.  It 
has  a  violet  color  which  is  due  to  the  burning  of  some  of  the  po- 
tassium. The  gas  given  off  in  these  experiments  is  either  burned 
at  once  or  escapes  into  the  air.  In  the  case  of  the  potassium  the 
action  takes  place  rapidly,  and  the  heat  evolved  is  sufficient  to  set 
fire  to  the  gas.  In  the  case  of  the  sodium  the  heat  evolved  does 
not  set  fire  to  the  gas.  In  order  to  collect  it  unburned,  it  is  only 
necessary  to  allow  the  decomposition  to  take  place,  so  that  the 
gas  will  rise  in  an  inverted  vessel  filled  with  water.  For  this 
purpose  fill  a  good-sized  test-tube  with  water  and  invert  it  in  a 
vessel  of  water.  Cut  off  a  piece  of  sodium  not  larger  than  a  pea, 
wrap  it  in  a  layer  or  two  of  filter-paper,  and  with  the  fingers  or 
a  pair  of  curved  forceps  bring  it  quickly  below  the  mouth  of  the 
test-tube  and  let  it  go.  It  will  rise  to  the  top,  the  decomposition 
of  the  water  will  take  place  quietly,  and  the  gas  formed,  being 
unable  to  escape,  will  remain  in  the  tube.  By  repeating  this 
operation  in  the  same  tube  a  second  portion  of  gas  may  be  made, 
and  so  on  until  enough  has  been  collected. 

Examine  the  gas  and  see  whether  it  acts  like  the  hydrogen 
obtained  from  water  by  means  of  the  electric  current.  What 
evidence  have  you  that  they  are  the  same  ?  Is  this  evidence  suf- 
ficient to  prove  the  identity  of  the  two  ?  Examine  the  water  on 
which  the  sodium  or  potassium  has  acted.  Wet  the  fingers  with 
it  and  rub  them  together.  Taste  the  water.  Does  it  change  the 
color  of  red  litmus  paper  ? 

Action  of  Sodium  and  Potassium  on  Water, — The  ex- 
planation of  the  action  of  sodium  and  potassium  on  water 
will  be  given  later.  Suffice  it  for  the  present  to  say  that 
water  consists  of  hydrogen  and  oxygen,  and  that  when 
sodium  comes  in  contact  with  it  this  element  takes  the 
place  of  some  of  the  hydrogen,  forming  the  compound 
sodium  hydroxide  or  caustic  soda.  The  action  of  potas- 
sium is  of  the  same  kind.  The  product  is  potassium 
hydroxide  or  caustic  potash. 


DECOMPOSITION  OP  WATER. 


41 


Decomposition  of  Water  by  Iron. — Some  metals  that  do 
not  decompose  water  at  ordinary  temperatures,  or  that 
decompose  it. slowly,  do  so  easily  at  elevated  temperatures, 
This  is  true  of  iron.  If  steam  is  passed  through  a  tube 
containing  pieces  of  iron  heated  to  redness,  decomposition 
of  the  water  takes  place,  the  oxygen  is  retained  by  the 
iron,  which  enters  into  combination  with  it,  while  the 
hydrogen  is  liberated. 

EXPERIMENT  28. — In  this  experiment  a  porcelain  tube  with  an 
internal  diameter  of  from  20  to  25  mm.  (about  an  inch)  and 
a  gas-furnace  are  desirable,  though  a  hard-glass  tube  and  a, 
charcoal-furnace  will  answer.  The  arrangement  of  the  apparatus 
is  shown  in  Fig.  11.  The  hydrogen  can  be  collected  by  displace- 


FlG.   11. 


The  products  formed 


ment  of  water,  as  in  the  case  of  oxygen, 
are  magnetic  oxide  of  iron  and  hydrogen. 

Decomposition  of  Water  by  Carbon  or  Charcoal. — Many 
other  substances  have  the  power  to  decompose  water  and 
set  hydrogen  free.  The  fact  that  a  combustible  gas  can 
be  obtained  from  water  has  led  to  many  attempts  to  manu- 
facture gas  for  heating  and  illuminating  purposes  from  this 
substance.  There  is,  however,  no  cheap  substance  that 
has  the  power  to  decompose  water  at  ordinary  tempera- 
tures. All  practicable  methods  involve  the  use  of  heat, 


42  INTRODUCTION   TO   CHEMISTRY. 

and  it  is  not  infrequently  the  case  that  the  quantity  of  heat 
required  to  effect  the  decomposition  is  greater  than  that 
which  would  be  obtained  by  burning  the  hydrogen  formed. 
In  the  manufacture  of  the  so-called  "water-gas"  which  is 
now  extensively  used  in  the  United  States  both  for  illumi- 
nating and  heating  purposes,  water  is  decomposed  by 
means  of  carbon  in  the  form  of  hard  coal.  Two  gaseous 
products  are  formed,  both  of  which  burn.  They  are  carbon 
monoxide,  or  carbonic  oxide,  and  hydrogen.  This  subject 
will  be  more  fully  discussed  under  the  head  of  carbon 
monoxide. 

Action  of  Acids  upon  Metals. — By  far  the  most  conven- 
ient method  for  making  hydrogen  consists  in  treating  a 
metal  with  an  acid.  As  will  be  seen  later,  acids  are  sub- 
stances that  contain  hydrogen,  and  are  characterized  by 
the  fact  that  they  give  up  this  hydrogen  very  easily  and 
take  up  other  elements  in  the  place  of  it.  Among  the 
common  acids  found  in  every  laboratory  are  hydrochloric 
acid,  sulphuric  acid,  and  nitric  acid.  The  chemistry  of 
these  compounds  will  be  taken  up  in  due  time;  but  as  we 
shall  be  obliged  to  use  them  before  they  are  studied 
systematically,  a  few  words  in  regard  to  them  are  desirable 
at  this  time. 

Hydrochloric  acid  is  a  compound  of  hydrogen  and 
chlorine.  It  is  a  gas  that  dissolves  easily  in  water.  It  is 
this  solution  that  we  use  in  the  laboratory.  It  is  manu- 
factured in  large  quantities.  It  is  frequently  called  "  muri- 
atic acid/' 

Sulphuric  acid  is  a  compound  of  sulphur,  oxygen,  and 
hydrogen.  It  is  an  oily  liquid  and  is  frequently  called 
"  oil  of  vitriol."  It  is  manufactured  in  very  large  quanti- 
ties, as  it  plays  an  important  part  in  many  of  the  most 
large  chemical  industries. 

Nitric  acid  is  a  compound  containing  nitrogen,  oxygen, 


ACTION  OF  ACIDS  UPON  METALS. 


43 


and  hydrogen.     When  pure,  it  is  a  colorless  liquid,  though 
as  we  get  it  it  is  commonly  colored  somewhat  yellow. 

When  a  metal,  as  zinc,  is  brought  in  contact  with 
hydrochloric  or  sulphuric  acid,  an  evolution  of  gas  takes 
place  at  once. 

EXPERIMENT  29. — In  a  cylinder  or  test-tube  put  some  small 
pieces  of  zinc,  and  pour  upon  it  some  ordinary  hydrochloric  acid. 
After  the  action  has  continued  for  a  minute  or  two  apply  a 
lighted  match  to  the  mouth  of  the  vessel.  The  gas  will  take •  fire 
and  burn.  If  sulphuric  acid  diluted  with  five  or  six  times  its 
volume  of  water  *  is  used  instead  of  hydrochloric  acid,  the  same 


4 

* 


FIG.  12.  FIG.  13. 

result  will  be  reached.    The  gas  evolved  is  hydrogen.    For  the 
purpose  of  collecting  the  gas  the  operation  is  best  performed  in  a 

*  If  it  is  desired  to  dilute  ordinary  concentrated  sulphuric  acid 
with  water,  the  acid  should  be  poured  slowly  into  the  water  while 
the  mixture  is  constantly  stirred.  If  the  water  is  poured  into  the 
acid,  the  heat  evolved  at  the  place  where  the  two  come  in  contact 
may  be  so  great  as  to  convert  the  water  into  steam  and  cause  the 
acid  to  spatter. 


44  INTRODUCTION   TO   CHEMISTRY. 

bottle  with  two  necks  called  a  Woulffs  flask  (see  Fig.  12),  or  in  a 
wide-mouthed  bottle  in  which  is  fitted  a  cork  with  two  holes  (see 
Fig.  13).  Through  one  of  the  holes  passes  a  funnel-tube,  and 
through  the  other  a  glass  tube  bent  in  a  convenient  form. 

The  zinc  used  is  granulated.  This  is  prepared  by  melting  zinc 
in  a  ladle  and  pouring  the  molten  metal  from  an  elevation  of 
four  or  five  feet  into  water.  The  advantage  of  this  form  is  that 
it  presents  a  large  surface  to  the  action  of  the  acids.  A  handful 
of  this  zinc  is  introduced  into  the  bottle,  arid  enough  of  a  cooled 
mixture  of  sulphuric  acid  and  water  (1  volume  concentrated  acid 
to  6  volumes  water)  poured  upon  it  to  cover  it.  Usually  a  brisk 
evolution  of  gas  takes  place  at  once.  Wait  for  two  or  three 
minutes,  and  then  collect  some  of  the  gas  by  displacement  of 
water.  When  the  action  becomes  slow,  add  more  of  the  dilute 
acid.  It  will  be  well  to  fill  several  cylinders  and  bottles  with  the 
gas,  and  also  a  gasometer,  from  which  it  can  be  taken  as  it  is 
needed  for  experiments. 

When  zinc  acts  upon  hydrochloric  acid  it  takes  the  place  of  the 
hydrogen  in  the  hydrochloric  acid  and  forms  the  compound  zinc 
chloride  : 

Zinc  +  Hydrochloric  Acid  =  Zinc  Chloride  +  Hydrogen  ; 

°r  Zinc  +  Hydrogen  )  =  Zinc         ,       Hydrogen. 

Chlorine    )       Chlorine  \ 

When  zinc  acts  upon  sulphuric  acid,  it  takes  the  place  of  the 
hydrogen  and  forms  the  compound  zinc  sulphate  : 

Zinc  +  Sulphuric  Acid  =  Zinc  Sulphate  +  Hydrogen  ; 

or  Sulphur     -\       Sulphur  \ 

Zinc  -}-  Oxygen      (  =  Oxygen   (  +  Hydrogen. 
Hydrogen )       Zinc        ) 

EXPERIMENT  30. — After  the  action  is  over  pour  the  contents  of 
the  flask  through  a  filter  into  an  evaporating-dish,  and  boil  off 
the  greater  part  of  the  water,  so  that,  on  cooling,  some  of  the 
substance  contained  in  solution  will  be  deposited.  If  the  opera- 
tion is  carried  on  properly,  the  substance  will  be  deposited  in 
regular  forms  called  crystals.  ItJs  zinc  sulphate. 


PHYSICAL  PROPERTIES  OF  HYDROGEN. 


45 


Physical  Properties  of  Hydrogen. — Hydrogen  is  a  color- 
less, inodorous,  tasteless  gas.  Made  by  the  action  of  zinc 
on  acids,  it  has  a  slightly  disagreeable  odor.  This  is  due 
to  the  presence  of  impurities.  If  it  is  passed  through 
certain  substances  that  have  the  power  to  destroy  the 
impurities,  the  odor  is  destroyed. 

EXPERIMENT  31.— Pass  some  of  the  gas  through  a  wash-cylinder 
containing  a  solution  of  potassium  permanganate;  collect  some 
of  it,  and  notice  whether  it  has  an  odor  or  not.  The  apparatus 
should  be  arranged  as  shown  in  Fig.  14.  The  solution  of  potas- 


4 


FIG.  14. 

sium  permanganate  is,  of  course,  contained  in  the  small  cylinder 
A,  and  the  tubes  are  so  arranged  that  the  gas  bubbles  through  it. 

The  gas  is  not  poisonous,  and  may  therefore  be  inhaled 
with  impunity.  We  could  not,  however,  live  in  an  atmos- 
phere of  hydrogen,  as  oxygen  is  essential  to  life.  It  is  the 
lightest  known  substance,  being  very  nearly  fourteen  and 
a  half  times  lighter  than  the  air  and  sixteen  times  lighter 


46 


INTRODUCTION   TO   CHEMISTRY. 


than  oxygen.     Its  lightness  may  be  shown  by  a  number  of 
simple  experiments. 

EXPERIMENT  32. — Place  a  vessel  containing  hydrogen  with  the 
mouth  upward  and  uncovered.  In  a  short  time  examine  the  gas, 
and  see  whether  it  is  hydrogen. 

EXPERIMENT  33. — Gradually  bring  a  vessel  containing  hydrogen 
with  its  mouth  upward  below  an  inverted  vessel  containing  air, 
in  the  way  shown  in  Fig.  15.  The  air  will  be  displaced.  On  ex- 


Fio.  15. 

amination  the  inverted  vessel  will  be  found  to  contain  hydrogen, 
while  the  one  with  the  mouth  upward  will  contain  none.  The 
gas  is  thus  poured  upwards. 

EXPERIMENT  34.— Soap-bubbles  filled  with  hydrogen  rise  in 
the  air.  This  experiment  is  best  performed  by  connecting  an 
ordinary  clay  pipe  by  means  of  a  piece  of  rubber  tubing  with  the 
exit-tube  of  a  gasometer  filled  with  hydrogen.  Small  balloons  of 
collodion  are  also  made  for  the  purpose  of  showing  the  lightness 
of  hydrogen. 

Balloons  are  always  filled  with  hydrogen,  or  some  other 
light  gas.  Some  kinds  of  illuminating  gas  are  rich  in 
hydrogen,  and  may  therefore  be  used  for  the  purpose. 

A  litre  of  hydrogen  at  0°  (Centigrade),  and  under  the 
pressure  of  760  mm.  (mercury),  weighs  0.08995  gram.  Its 
specific  gravity  is  0.0696.  A  comparison  of  these  figures 
with  the  corresponding  figures  for  oxygen  leads  to  an  in- 
teresting observation.  The  weight  of  a  litre  of  oxygen  is 
1.429  grams;  its  specific  gravity  is  1.1056.  The  ratio  of 


CHEMICAL    PROPERTIES   OF  HYDROGEN.  47 

the  weights  of  equal  volumes  of  hydrogen  and  oxygen  to 
each  other  is  very  nearly  1  :  16,  or 

0.08995  :  1.429  ::  1  :  nearly  16. 

At  a  very  low  temperature  and  high  pressure,  it  can  be 
converted  into  a  liquid  that  boils  at  —  252 p.  It  cannot 
be  liquefied  at  any  temperature  above  —  242°,  no  matter 
what  pressure  it  may  be  subjected  to. 

Chemical  Properties  of  Hydrogen,  —  Under  ordinary 
circumstances,  hydrogen  is  not  a  particularly  active  ele- 
ment. It  does  not  unite  with  oxygen  at  ordinary  tempera- 
tures, but,  like  wood  and  most  other  combustible 
substances,  it  must  be  heated  to  the  kindling  temperature 
before  it  will  burn.  We  have  seen  that  it  burns  when  a 
lighted  match  is  applied  to  it.  The  flame  is  colorless,  or 
slightly  blue.  As  burned  under  ordinary  circumstances, 
the  flame  is  colored  in  consequence  of  the  presence  of  ' 
foreign  substances ;  but  that  it  is  colorless  when  the  gas  is 
burned  alone  can  be  shown  by  burning  it  from  a  platinum 
tube,  which  is  itself  not  acted  upon  by  the  heat. 

EXPERIMENT  35. — If  there  is  no  small  platinum  tube  available, 
roll  up  a  small  piece  of  platinum  foil  and  melt  it  into  the  end  of 
a  glass  tube,  as  shown  in  Fig.  16.  Connect  the 
burner  thus  made  with  the  gasometer  containing 
hydrogen,  and  after  the  gas  has  been  allowed  to 
issue  from  it  for  a  moment,  set  fire  to  it.  In  a 
short  time  it  will  be  seen  that  the  flame  is  practi- 
cally colorless  and  gives  no  light.  That  it  is  hot 
can  be  shown  by  holding  a  piece  of  platinum  wire 
or  a  piece  of  some  other  metal  in  it. 

Hydrogen  burns.     We  have  seen  that  what 
we  call  burning  consists  in  combining  with 
oxygen.     On  the  other  hand,  substances  that        FlG  16- 
burn  in  the  air  are  extinguished  when  put  into  a  vessel  con- 


INTRODUCTION    TO   CHEMISTRY. 


taining  hydrogen.  This  is  equivalent  to  saying  that  a  sub- 
stance that  is  uniting  with  oxygen  does  not  continue  to 
unite  with  oxygen  when  put  in  an  atmos- 
phere of  hydrogen,  and  does  not  combine 
with  the  hydrogen.  This  is  expressed  by 
saying  that  hydrogen  does  not  support 
combustion.  The  following  experiment 
shows  this. 

EXPERIMENT  36. — Hold  a  cylinder  filled  with 
hydrogen  with  the  mouth  downward.  Insert 
into  the  vessel  a  lighted  taper  fixed  on  a  bent 
wire,  as  shown  in  Fig.  17.  The  gas  will  take 
fire  at  the  inouth  of  the  vessel,  but  the  taper 
will  be  extinguished.  On  withdrawing  the 
taper  and  holding  the  wick  for  a  moment  in 
the  burning  hydrogen,  it  will  take  fire,  but  on 
putting  it  back  in  the  hydrogen  it  will  again 
be  extinguished.  Other  burning  substances 
should  be  tried  in  a  similar  way. 


FIG.  17. 


Product  Formed  when  Hydrogen  Burns  in  Oxygen. — As 
when  hydrogen  burns  it  combines  with  oxygen,  a  product 
should  be  obtained  in  which  both  hydrogen  and  oxygen  are 
present.  In  the  experiments  performed  we  have  seen  no 
evidence  of  the  formation  of  such  a  product,  simply  for  the 
reason  that  when  formed  it  is  an  invisible  gas,  and,  though 
it  can  easily  be  condensed  to  a  liquid,  no  precautions  were 
taken  to  get  it  in  this  form.  The  product  is,  in  fact, 
ordinary  water,  which  we  shall  next  study. 


CHAPTER   IV. 
COMBINATION  OF  HYDROGEN  AND  OXYGEN.— WATER. 

WATER  was  regarded  as  an  element  until,  towards  the 
end  of  the  last  century,  the  discovery  of  hydrogen  and 
oxygen,  and  of  the  nature  of  combustion,  led  to  the  dis- 
covery of  its  composition. 

Occurrence. — The  wide  distribution  of  water  on  the  earth 
is  familiar  to  every  one.  But  water  also  occurs  in  forms 
and  conditions  which  prevent  its  immediate  recognition. 
Thus  all  living  things  contain  a  large  proportion  of  water, 
which  can  be  driven  off  by  heat.  If  a  piece  of  wood  or  a 
piece  of  meat  is  heated,  water  passes  off. 

EXPERIMENT  37. — In  a  dry  tube  heat  gently  a  small  piece  of 
wood.  What  evidence  do  you  obtain  that  water  is  given  off  ?  Do 
the  same  thing  with  a  piece  of  fresh  meat. 

The  proportion  of  water  in  animal  and  vegetable  sub- 
stances is  very  great.  If  the  body  of  a  man  weighing  150 
pounds  should  be  put  in  an  oven  and  thoroughly  dried, 
there  would  be  left  only  about  40  pounds  of  solid  matter, 
all  the  rest  being  water.  As  all  meat,  vegetables,  and 
food-stuffs  in  general  contain  a  similar  large  propor- 
tion of  water,  it  is  evident  that  water  is  an  important 
article  of  commerce.  When  we  buy  four  pounds  of  beef, 
we  pay  for  about  three  pounds  of  water  and  one  of  solid 
matter.  ^ 

49 


50  INTRODUCTION   TO   CHEMISTRY. 

Water  of  Crystallization. — Water  also  occurs  in  another 
form  in  which  it  does  not  easily  reveal  its  presence.  This 
is  as  water  of  crystallization. 

EXPERIMENT  38. — Take  some  of  the  crystals  of  zinc  sulphate 
obtained  in  Experiment  30.  Spread  them  out  on  a  layer  of  filter- 
paper,  and  finally  press  two  or  three  of  them  between  folds  of 
the  paper.  Examine  them  carefully.  They  appear  to  be  quite 
dry,  and  in  the  ordinary  sense  they  are  dry.  Put  them  into  a 
dry  tube,  and  heat  them  gently.  What  evidence  do  you  obtain 
of  the  giving  off  of  water  ?  Describe  the  changes  which  the  crys- 
tals undergo. 

EXPERIMENT  39. — Perform  a  similar  experiment  with  some 
gypsum,  which  is  the  natural  substance  from  which  "  plaster  of 
Paris  "  is  made. 

EXPERIMENT  40.— Heat  a  few  small  crystals  of  copper  sulphate 
or  blue  vitriol.  What  evidence  of  water  ?  Describe  the  changes 
in  the  crystals.  After  no  further  change  takes  place,  dissolve 
what  is  left  in  a  little  water.  What  is  the  color  of  the  solution  ? 
Evaporate  to  the  point  of  crystallization.  How  do  the  crystals 
obtained  compare  with  those  first  taken  ? 

Many  compounds  when  deposited  from  solutions  in 
water  in  the  forni  of  crystals  combine  with  definite  quan- 
tities of  water.  This  water  is  not  present  as  such,  but  is 
held  in  chemical  combination.  Hence  the  substance  does 
not  appear  moist,  though  it  may  contain  more  than  half 
its  weight  of  water.  This  water  of  crystallization  is,  in 
some  way  which  we  do  not  understand,  essential  to  the 
form  of  the  crystal.  If  it  is  driven  oif  by  heat,  the  crystal 
falls  to  pieces.  Some  compounds  combine  under  different 
circumstances  with  different  quantities  of  water,  the  form 
of  the  crystals  varying  with  the  quantity  of  water  in  com- 
bination. 

Efflorescence. — Compounds  differ  greatly  as  regards  the 
ease  with  which  they  give  up  water  of  crystallization.  In 
general,  it  is  given  off  when  the  compound  containing  it  is 
heated  to  the  temperature  of  boiling  water.  But  some 


ANALYSIS  AND  SYNTHESIS.  51 

compounds  give  it  up  by  simple  contact  with  the  air.  This 
is  true  of  sodium  sulphate,  or  Glauber's  salt,  which  con- 
tains about  56  per  cent  of  water  of  crystallization. 

EXPERIMENT  41. — Select  a  few  crystals  of  sodium  sulphate 
which  have  not  lost  their  lustre.  Put  them  on  a  watch-glass, 
and  let  them  lie  exposed  to  the  air  for  an  hour  or  two.  What 
change  takes  place  in  their  appearance  ?  How  does  this  change 
compare  with  that  of  the  crystals  of  zinc  sulphate  ? 

Compounds  which  lose  their  water  of  crystallization  by 
simple  contact  with  the  air  are  said  to  effloresce.  They  are 
called  efflorescent. 

Deliquescence. — Some  compounds  if  deprived  of  their 
water  of  crystallization  will  take  it  up  again  when  allowed 
to  lie  in  an  atmosphere  containing  moisture.  As  the  air 
always  contains  moisture,  it  is  only  necessary  to  expose 
such  compounds  to  the  air  in  order  to  notice  the  phe- 
nomenon. It  is  well  shown  by  the  compound  calcium 
chloride.  This  substance  has  a  remarkable  power  of 
attracting  water  to  itself  and  holding  it  in  combination. 

EXPERIMENT  42.— Expose  a  few  pieces  of  calcium  chloride  to 
the  air  for  some  hours.  Describe  the  changes  that  take  place. 

Substances  that  absorb  water  from  the  air  and  dissolve 
in  this  water  are  said  to  deliquesce.  They  are  called  deli- 
quescent. 

Analysis  and  Synthesis. — In  order  to  determine  the 
composition  of  water,  or  of  any  other  'compound,  we  must 
analyze  it.  We  may  simply  determine  what  substances 
enter  into  its  composition  without  determining  the  relative 
quantities  of  these  substances.  In  this  case  we  make  what 
is  called  a  qualitative  analysis.  If,  however,  we  not  only 
determine  what  substances  are  present,  but  also  in  what 
proportion  they  are  present,  we  then  make  a  quantitative 
analysis. 


5 2  INTRODUCTION    TO   CHEMISTRY. 

The  composition  of  a  substance  may  also  be  determined 
by  putting  together  its  constituents  and  causing  them  to 
combine  chemically.  An  operation  of  this  kind  is  called 
a  synthesis.  A  synthesis,  then,  is  the  opposite  of  an 
analysis.  Just  as  we  may  make  a  qualitative  or  a  quanti- 
tative analysis,  so  also  we  may  make  a  qualitative  or  a 
quantitative  synthesis.  These  processes  are  well  illustrated 
in  the  operations  necessary  to  determine  the  composition 
of  water. 

Decomposition  of  Water  by  the  Electric  Current  and 
what  it  Teaches. — That  water  contains  hydrogen  and 
oxygen  has  already  been  shown  in  Experiment  4.  It  will 
now  be  well  to  repeat  the  experiment  and  see  whether  we 
can  learn  anything  more  regarding  the  composition  of 
water  than  that  it  contains  hydrogen  and  oxygen.  In  the 
first  place,  the  question  suggests  itself.  In  what  proportions, 
by  weight  and  by  volume,  are  the  gases  combined  ? 

EXPERIMENT  43. — The  tubes  in  the  apparatus  used  in  Experi- 
ment 4,  or  some  other  similar  apparatus,  should  be  marked  by 
means  of  a  file,  or  by  etching,  so  that  equal  divisions  can  be  rec- 
ognized. Tubes  thus  divided  so  that  the  divisions  indicate  cubic 
centimetres  are  most  convenient  for  the  purpose.  Let  the  gases 
formed  by  the  action  of  the  electric  current,  as  in  Experiment  4, 
rise  in  the  graduated  tubes,  and  observe  the  volumes.  It  will  be 
seen  that  when  one  tube  is  just  full  of  gas,  the  other,  if  it  is  of 
the  same  size,  will  be  only  half  full.  On  examining  the  gases  the 
larger  volume  will  be  found  to  be  hydrogen,  and  the  smaller  vol- 
ume oxygen.  This  experiment  has  been  performed  an  untold 
number  of  times  and  always  with  the  same  result. 

The  relative  weights  of  equal  volumes  of  the  two  gases 
are  known,  so  that  the  relative  weights  of  the  gases  obtained 
from  water  by  the  action  of  the  electric  current  can  easily 
be  calculated.  The  ratio  of  the  weights  of  equal  volumes 
of  hydrogen  and  oxygen  is  1  :  15.88.  Therefore,  if  two 
volumes  of  hydrogen  are  combined  with  one  volume  of 


SYNTHESIS   OF  WATER  BY  BURNING   HYDROGEN.      53 

oxygen,  the  ratio  between  the  weights  is  2  : 15. 88  or  1  :  7.94. 
Although  the  above  experiment  shows  that  hydrogen  and 
oxygen  are  obtained  from  water  in  the  proportion  of  two 
volumes  of  the  former  to  one  of  the  latter,  or  of  one  part 
by  weight  of  the  former  to  nearly  eight  parts  by  weight  of 
the  latter,  the  experiment  does  not  prove  that  this  is  the 
actual  composition  of  water.  For  it  may  be  that  other 
elements  besides  hydrogen  and  oxygen  are  contained  in 
the  water,  and  it  may  be  that  all  the  hydrogen  and  oxygen 
are  not  set  free  by  the  action  of  the  electric  current. 
Whether  either  of  these  possibilities  is  true  might  be 
determined  by  decomposing  a  weighed  quantity  of  water, 
and  weighing  the  hydrogen  and  oxygen  obtained  from  it. 
If  it  should  be  found  that  the  sum  of  the  weights  of 
hydrogen  and  oxygen  is  equal  to  the  weight  of  the  water 
decomposed,  this  fact  would  be  evidence  that  only 
hydrogen  and  oxygen  are  contained  in  water,  and  that 
they  are  present  in  the  proportions  stated. 

.  Synthesis  of  Water  by  Burning  Hydrogen. — That  water 
consists  of  hydrogen  and  oxygen  only  can  be  satisfactorily 
proved  by  effecting  its  synthesis.  In  the  first  place,  it  can 
be  shown  that  water  is  formed  when  hydrogen  burns  in 
the  air,  and,  as  it  has  been  shown  that  burning  is  combin- 
ing with  oxygen,  the  conclusion  is  justified  that  water 
consists  of  hydrogen  and  oxygen. 

EXPERIMENT  44.— Pass  hydrogen  from  a  generating-flask  or  a 
gasometer  through  a  tube  containing  some  substance  that  will 
absorb  moisture,  for  all  gases  made  in  the  ordinary  way  and  col- 
lected over  water  are  charged  with  moisture.  We  have  seen  in 
Experiment  42  that  calcium  chloride  has  the  power  to  absorb 
moisture.  It  is  extensively  used  in  the  laboratory  for  the  purpose 
of  drying  gases,  and  it  may  be  used  in  the  present  experiment. 
It  should  be  in  granulated  form,  not  powdered.  After  passing 
the  hydrogen  through  the  calcium  chloride,  pass  it  through  a 
tube  ending  in  a  narrow  opening,  and  set  fire  to  it.  If  now  a  dry 


54  INTRODUCTION    TO   CHEMISTRY. 

vessel  is  held  over  the  flame,  drops  of  water  will  condense  on  its 
surface  and  run  down.  A  convenient  arrangement  of  the  appa- 
ratus is  shown  in  Fig.  18. 


FIG.  18. 

A  is  the  calcium  chloride  tube.  Before  lighting  the  jet  hold  a 
glass  plate  in  the  escaping  gas,  and  see  whether  water  is  deposited 
on  it.  Light  the  jet  before  putting  it  under  the  bell-jar,  other- 
wise if  hydrogen  is  allowed  to  escape  into  the  vessel  it  will  con- 
tain a  mixture  of  air  and  hydrogen,  and  this  mixture,  as  will  soon 
be  seen,  is  explosive. 

Synthesis  o£  Water  by  Mixing  Hydrogen  and  Oxygen, 

—If  hydrogen  and  oxygen  are  mixed  together,  and  the 
mixture  is  allowed  to  stand  unmolested,  it  remains  un- 
changed. If,  however,  a  spark  or  a  flame  is  brought  in 
contact  with  the  mixture,  a  violent  explosion  occurs,  and 
a  careful  examination  has  shown  that  the  explosion  is  the 
result  of  the  combination  of  the  two  gases.  The  noise  its 
caused  by  the  sudden  great  expansion  of  the  gases  occa- 
sioned by  the  development  of  heat.  This  expansion  is 
instantly  followed  by  a  contraction. 

EXPERIMENT  45. — Mix  hydrogen  and  oxygen  in  the  proportion 
of  about  2  volumes  of  hydrogen  to  1  volume  of  oxygen  in  a  gas- 


QUANTITATIVE  SYNTHESIS   OF  WATER.  55 

ometer.  Fill  soap-bubbles,  as  directed  in  Experiment  34,  with 
this  mixture  and  allow  them  to  rise  in  the  air.  As  they  rise 
bring  a  lighted  taper  in  contact  with  them,  when  a  sharp  explosion 
will  occur.  Great  care  must  be  taken  to  keep  all  flames  away 
from  the  vicinity  of  the  gasometer  and  the  end  of  the  delivery- 
tube.  This  experiment  may  be  conveniently  performed  by  hang- 
ing up,  about  six  to  eight  feet  above  the  experiment-table,  a 
good-sized  tin  funnel-shaped  vessel  with  the  mouth  downward. 
Now  place  a  gas  jet  or  a  small  flame  of  any  kind  at  the  mouth  of 
the  vessel.  If  the  soap-bubbles  are  allowed  to  rise  below  this 
apparatus  they  will  come  in  contact  with  flame  and  explode  at 
once.* 

This  experiment  simply  shows  that  a  mixture  of  hydrogen 
and  oxygen  explodes  when  brought  in  contact  with  a  flame, 
and  that  the  gases  do  not  act  upon  each  other  at  ordinary 
temperatures. 

Quantitative  Synthesis  of  Water. — In  order  to  show  that 
when  the  explosion  occurs  water  is  formed,  and  in  what 
proportions  the  gases  combine,  it  is  necessary  to  work  in 
closed  vessels  so  constructed  as  to  permit  accurate  measure- 
ment of  the  volumes  of  the  gases.  The  experiment  is  so 
important  that,  if  possible,  it  should  be  performed  by 
the  teacher  before  the  class.  The  vessel  in  which  the 
gases  are  brought  together  and  caused  .to  combine  is 
called  a  eudiometer  (from  evdia,  calm  air,  and  fAerpov,  a 
measure).  It  is  simply  a  tube  graduated  in  millimetres 


FIG.  19 

and  having  two  small  platinum  wires  passed  through  it  at 
the  closed  end,  nearly  meeting  inside  and  ending  in  loops 
outside,  as  shown  in  Fig.  19.  The  eudiometer  is  filled  with 
mercury,  inverted  in  a  mercury  trough,  and  held  in  an 

*  The  same  apparatus  may  be  used  in  experimenting  with  soap- 
bubbles  filled  with  hydrogen. 


56  INTRODUCTION   TO   CHEMISTRY. 

upright  position  by  means  of  proper  clamps.  A  quantity 
of  pure  hydrogen  is  passed  np  into  the  tube  and  its  volume 
accurately  measured.  About  half  this  volume  of  oxygen 
is  then  introduced  and  accurately  measured,  and  after  the 
mixture  has  been  allowed  to  stand  for  a  few  minutes,  a 
spark  is  passed  between  the  wires  in  the  eudiometer  by 
connecting  the  loops  with  the  poles  of  a  small  Kuhmkorff 
coil  or  with  a  Leyden  jar.  Under  these  circumstances  the 
explosion  takes  place  noiselessly  and  with  very  little 
danger.  If  the  interior  of  the  tube  was  dry  before  the 
explosion,  it  will  be  seen  to  be  moist  afterwards,  and  a 
marked  decrease  in  the  volume  of  the  gases  is  also  observed. 
That  water  is  the  product  of  the  action  has  been  proved 
beyond  any  possibility  of  a  doubt,  over  and  over  again. 
As  the  liquid  water  which  is  formed  occupies  an  inap- 
preciable volume  as  compared  with  the  volume  of  the 
gases  which  combine,  the  decrease  in  volume  represents 
the  total  volume  of  hydrogen  and  oxygen  which  have  com- 
bined. Now,  if  the  experiment  is  performed  with  the  two 
gases  in  different  proportions,  it  will  be  found  that  only 
when  they  are  mixed  in  the  proportion  of  two  volumes  of 
hydrogen  and  one  volume  of  oxygen  do  they  completely 
disappear  in  the  explosion.  If  hydrogen  is  present  in 
larger  proportion,  the  excess  is  left  over.  If  oxygen  is 
present  in  larger  proportion,  the  excess  of  oxygen  is  left 
over.  It  appears,  therefore,  that  when  hydrogen  and 
oxygen  combine  to  form  water,  they  do  so  in  the  propor- 
tion of  two  volumes  of  hydrogen  to  one  volume  of  oxygen. 
In  order  that  the  student  may  fully  appreciate  this  experi- 
ment, it  is  desirable  that  he  should  at  this  point  familiarize 
himself  with  the  precautions  necessary  in  measuring  the 
volumes  of  gases,  if  he  has  not  already  done  so. 

Law  of  Dalton  and  Gay  Lussac — Correction   for   Tem- 
perature,— The  volume  of  a  gas  varies  with  the  tempera- 


BOYLE'S  LAW.  57 

ture  and  pressure.  When  the  temperature  of  a  gas  is 
raised  one  degree  Centigrade  its  volume  is  increased  -^ 
part  of  the  volume  occupied  by  it  at  0°.  If,  therefore,  the 

volume  of  a  gas  at  0°  is  F,  at  t°  its  volume  v  will  be 

i 

F+^.F,    or    »=F+A..F. 

This  expression  may  also  be  written 

v=  F -f  0.00366*  x  F,    or    v  =  F(l  -f-  0.00366*). 
From  this  it  follows  that 


"4.  +  0.00366** 

This  is  the  law  of  Dalton  and  Gay  Lussac  as  it  was  dis- 
covered by  them  simultaneously  in  1801. 

It  is  customary  to  reduce  the  observed  volume  of  a  gas 
to  the  volume  which  it  would  have  at  0°.  The  correction 
is  made  in  accordance  with  the  above  expression.  Thus, 
if  the  volume  of  a  gas  is  found  to  be  250  cubic  centi- 
metres at  15°,  and  it  is  required  to  find  what  its  volume 
would  be  at  0°,  the  calculation  is  made  thus:  In  this 
case  v,  the  observed  volume,  ,is  250  cc. ;  *,  the  tempera- 
ture, is  15°.  Substituting  these  values  in  the  equation 

V  —  v 

~  1  +  0.00366*'  ^ 


1  +  0.00366  X  15' 
from  which  we  get  236.99  as  the  value  of  F. 

Boyle's  Law. — But  the  volume  of  a  gas  varies  also 
according  to  the  pressure.  When  the  pressure  is  doubled, 
the  volume  is  decreased  to  one  half;  and  when  the  pressure 


5  8  INTRODUCTION    TO  CHEMISTRY. 

is  decreased  to  one  half,  the  volume  is  doubled;  and  so 
on.  In  other  words,  the  volume  of  a  gas  is  inversely  pro- 
portional to  the  pressure.  Increase  the  pressure  two. 
three,  or  four  times  and  the  volume  becomes  one  half,  one 
third,  or  one  fourth,  and  vice  versa.  If  the  gas  has  the 
volume  F  at  the  pressure  P,  and  at  pressure  p  the  vohime 
v,  these  values  bear  to  one  another  the  relations  expressed 
in  the  equation 


This  law  was  discovered  by  Boyle  in  1660  and  is  called 

Boyle's  law. 

Correction  for  Pressure.  —  The  pressure  is  usually  stated 
in  millimetres,  and  reference  is  to  the  height  of  a  column 
of  mercury  to  which  the  pressure  corresponds.  A  gas 
contained  in  an  open  vessel,  or  in  a  vessel  over  mercury 
or  water,  in  which  the  level  of  the  liquid  inside  and  out- 
side the  vessel  is  the  same,  is 
under  the  pressure  of  the  atmos- 
phere. What  that  is  we  learn 
from  the  barometer.  As  this 
pressure  varies,  it  is  necessary 
to  read  the  barometer  whenever 
a  gas  is  measured,  and  then  to 
reduce  the  observed  volume  to 
certain  conditions  which  are  ac- 
cepted as  standard.  When  the 
gas  is  measured  in  a  tube  over 
mercury  or  water,  and  the  level 
of  the  liquid  inside  the  tube  is 
higher  than  that  outside,  the  gas 
is  under  diminished  pressure,  the 
amount  of  diminution  depending  on  the  height  of  the 


COMBINED   VOLUMETRIC  CORRECTIONS.  59 

column  of  mercury  or  water  in  the  tube.  Thus,  if  the 
arrangement  is  as  represented  in  Fig.  20,  and  the  height 
of  the  mercury  column  above  the  level  of  the  mercury 
in  the  trough  is  100  millimetres,  and  the  pressure  of  the 
atmosphere  is  760  millimetres,  then  the  gas  in  the  tube 
is  not  under  the  full  atmospheric  pressure,  for  the  atmos- 
pheric pressure  exerted  on  the  mercury  is  supporting  a 
column  of  mercury  100  millimetres  high,  and  the  pres- 
sure actually  brought  to  bear  on  the  gas  corresponds  to 
760  —  100  =  660  mm.  Suppose  that  in  this  case  the 
volume  of  gas  actually  measured  is  75  cc.  Call  this  v. 
What  would  be  the  actual  volume  V  of  the  gas  under  the 

standard  pressure  760  mm.  ?     We  have  seen  that 

" 

VP  =  vp. 
Now  P  =  760,     v  =  75,     and    p  =  660.     Therefore, 

760  V  =  75  x  660,     or     V=  75  *  66°  =  65.13. 

Combined  Volumetric  Corrections.  —  In  all  cases  it  is 
necessary  to  make  a  correction  similar  to  this  in  dealing 
with  the  volumes  of  gases.  The  correction  for  tempera- 
ture and  that  for  pressure  may  be  made  in  one  operation, 
the  formula  being 


__ 

~ 


__ 
760(273  +  1)'  ~  760(1  +  0.00366*)' 

in  which  V  =  the  volume  of  the  gas  at  0°  and  760  mm. 
pressure;  v  =  the  observed  volume;  t  =  the  observed  tem- 
perature; p  =  the  pressure  under  which  the  gas  is 
measured. 

Correction   for   Aqueous   Pressure.  —  The   presence    of 
water-vapor  in  a  gas  also  influences  its  volume,  and  this 


60  INTRODUCTION   TO  CHEMISTRY. 

must  be  taken  into  account.  The  formula  for  making  all 
the  corrections  required  in  determining  the  volume  of  a 
gas  is 

273v(p-a)  v(p-a) 

760(273  +  /)'  "  760(1  -f  0.00366*)' 

in  which  a  is  the  pressure  of  water-vapor  at  t°. 

[PROBLEMS. — The  volume  of  a  gas  contained  in  a  eudiometer 
measures  42  cc.  The  height  of  the  mercury  column  over  which 
it  stands  is  68  mm.  The  barometer  indicates  an  atmospheric 
pressure  of  746  mm.  The  temperature  is  18°  C.  What  would  be 
the  volume  of  the  gas  at  0°  and  760  mm.  pressure  ? 

The  volume  of  a  gas  contained  in  a  vessel  over  a  column  of 
mercury  85  mm.  high  measures  24  cc.  The  barometer  indicates 
a  pressure  of  774  mm.  The  temperature  is  19°.  What  would  be 
the  volume  of  the  gas  under  normal  conditions,  i.e.,  t  —  0°  and 
P=  760  mm.? 

The  volume  of  a  gas  contained  in  a  vessel  over  water,  the 
level  of  the  water  inside  and  outside  being  the  same :  v  =  80  cc. ; 
t  =  20°  ;  p  =  740  mm. ;  a  =  17.4  at  20°.  What  is  the  value  of  V 
or  the  volume  at  0°  and  760  mm.?] 

Apparatus  for  Measuring  the  Volume  of  a  Gas. — A  con- 
venient apparatus  for  measuring  gas-volumes  is  that  repre- 
sented in  Fig.  21.  It  consists  of  two  tubes  connected 
at  the  base  by  means  of  a  piece  of  rubber  tubing  and 
containing  water.  The  tube  A  is  graduated,  the  other 
is  not.  The  gas  to  be  measured  is  brought  into  the  tube 
A,  and  the  other  tube  is  then  placed  at  the  side  of  the  one 
containing  the  gas,  and  its  height  adjusted  so  that  the 
column  of  liquid  in  both  tubes  is  at  the  same  level.  Under 
these  circumstances,  obviously  the  gas  is  under  the  atmos- 
pheric pressure  for  which  the  necessary  correction  must, 
of  course,  be  made.  It  is  also  necessary  in  this  case  to 
make  the  corrections  for  temperature  and  for  the  pressure 


APPARATUS  FOR  MEASURING  THE  VOLUME  OF  A  GAS.  61 

of  water-vapor.  It  is,  further, 
sometimes  convenient  when  the 
gas  is  measured  over  water 
to  transfer  the  measuring-tube  to 
a  vessel  containing  enough  water 


B 


FIG.  21. 


FIG.  22. 

to  permit  the  immersion  of  the 
tube  to  a  point  at  which  the  level 
of  the  liquid  inside  and  outside  the 
tube  is  the  same.  In  this  case  the 
conditions  are  the  same  as  in  the 
apparatus  just  described.  The  ar- 
rangement is  shown  in  Fig.  22. 


62  INTRODUCTION  TO  CHEMISTRY. 

Calculation  of  the  Results  Obtained  on  Exploding  Mix- 
tures of  Hydrogen  and  Oxygen. — Having  determined  that 
whenever  hydrogen  and  oxygen  combine,  they  do  so  in  the 
proportion  1  volume  of  oxygen  to  2  volumes  of  hydrogen, 
and  that  when  they  combine,  the  volume  of  water  formed 
is  so  slight  as  to  amount  to  nothing  in  the  measurements, 
we  know  that  whenever  a  mixture  of  hydrogen  and  oxygen 
is  exploded,  no  matter  in  what  proportions  they  may  be 
present,  the  volume  of  gas  that  disappears  as  such  consisted 
of  2  volumes  of  hydrogen  and  1  volume  of  oxygen,  or,  in 
other  words,  one  third  of  the  volume  that  has  disappeared 
was  oxygen  and  two  thirds  hydrogen.  Take  this  example  : 
A  quantity  of  hydrogen  corresponding  to  60  cc.  under 
standard  conditions  is  introduced  into  a  eudiometer;  40  cc. 
of  oxygen  are  added.  What  contraction  will  there  be  on 
exploding  the  mixture  ?  Plainly  the  60  cc.  of  hydrogen 
will  combine  with  30  cc.  of  oxygen.  The  90  cc.  of  gas 
will  disappear,  and  the  10  cc.  of  oxygen  will  remain  un- 
changed. From  a  total  volume  of  100  cc.,  therefore,  we 
get  a  contraction  to  10  cc.  One  third  of  the  contraction 
represents  the  oxygen,  and  two  thirds  the  hydrogen. 

Synthesis  of  Water  by  Passing  Hydrogen  over  Heated 
Oxides. — The  synthesis  of  water  can  be  effected  by  passing 
hydrogen  over  a  compound  containing  oxygen  and  heated 
to  a  sufficiently  high  temperature.  A  convenient  substance 
for  this  purpose  is  the  compound  of  copper  and  oxygen 
known  as  copper  oxide  or  black  oxide  of  copper.  When 
hydrogen  is  passed  over  this  compound  at  ordinary  tem- 
peratures no  action  takes  place.  If,  however,  the  tempera- 
ture is  raised  to  low  redness  the  hydrogen  combines  with 
the  oxygen,  forming  water,  and  the  copper  is  left  behind 
as  such. 

EXPERIMENT  46. — Arrange  an  apparatus  as  shown  in  Fig.  23. 
A  is  a  Woulff's  flask  for  generating  hydrogen.     To  remove  irn- 


QUANTiTATWlB  SYNTHESIS  OF  WATER.  63 

purities  the  gas  is  passed  through  a  solution  of  potassium  per- 
manganate contained  in  the  wash-cylinder  B.  The  U  tube  C 
contains  granulated  calcium  chloride,  and  the  cylinder  D  contains 
concentrated  sulphuric  acid,  both  of  them  serving  to  remove 
moisture  from  the  gas.  The  pure  dry  hydrogen  is  now  passed 
through  the  hard-glass  tube  E,  which  contains  a  layer  of  copper 
oxide.  After  the  apparatus  is  filled  with  hydrogen  the  gas-jet  is 


FIG.  23. 

lighted  and  the  copper  oxide  heated  to  low  redness.  What  evi- 
dence do  you  obtain  of  the  formation  of  water  ?  What  change 
takes  place  in  the  color  of  the  substance  in  the  tube  ?  Try  the 
action  of  nitric  acid  on  a  little  of  the  black  oxide  of  copper,  and 
on  the  substance  left  after  the  action  of  the  hydrogen. 

Quantitative  Synthesis  of  Water. — In  this  case  the  loss 
in  weight  of  the  copper  oxide  represents  oxygen.  If, 
therefore,  we  should  weigh  the  copper  oxide  before  the 
experiment,  and  afterwards  the  copper,  and  should  also 
collect  and  weigh  the  water  formed,  we  could  from  the 
figures  obtained  easily  calculate  the  relative  weight  of  the 
oxygen  contained  in  the  water..  The  water  can  easily  be 
collected  by  passing  it  into  a  tube  filled  with  calcium 
chloride.  If  the  tube  is  weighed  before  the  experiment 
and  after  it,  the  gain  in  weight  will  represent  the  weight 


64  INTRODUCTION    TO   CHEMISTRY. 

of  the  water  collected.  All  these  weighings  can  be  made 
without  difficulty  on  a  chemical  balance  such  as  is  found 
in  every  chemical  laboratory.  Where  time  will  permit  it 
will  be  well  for  each  student  to  go  through  with  this  ex- 
periment. A  few  experiments  of  this  kind  will  serve  to 
impress  upon  the  mind  the  reality  of  the  quantitative  rela- 
tions about  which  he  is  constantly  hearing.  If  it  is 
performed,  a  small  hard-glass  tube  from  12  to  15  centi- 
metres (5  to  6  inches)  long  and  about  1  centimetre  (or 
half  an  inch)  internal  diameter  should  be  used  in  place 
of  the  tube  E  in  the  qualitative  experiment  above  described. 
The  tube  is  drawn  out  at  one  end  and  a  small  plug  of 
asbestos  put  in  the  small  end.  Connection  with  the 
weighed  calcium- chloride  tube  is  made  at  this  end.  The 
tube  is  first  thoroughly  dried.  Then  coarsely  granulated 
copper  oxide  (a  few  grams)  is  introduced  into  it  and  the 
whole  weighed.  After  the  experiment  the  tube  and  the 
copper  are  weighed  again.  The  calcium-chloride  tube 
should  of  course  be  weighed  before  and  after  the  experi- 
ment. The  results  are  calculated  thus : 

Let  x  =  weight  of  tube  -|-  copper  oxide  before  the 

experiment ; 

y  =  weight  of  tube  -j-  copper  after  the  ex- 
periment. 

Then  x  —  y  =  weight  of  oxygen  taken  from  the  copper 
oxide. 

Let  a  =  weight  of  calcium-chloride  tube  before; 

1=        "     "         "  "          "     after. 

Then  b  —  a  =  weight  of  water  formed. 

If  the  experiment  is   carefully  performed,   it  will  be 

/•vt    | n  i 

found  that  the  ratio  ,       y  is  very  nearly  4. 
1}  —  a 

Oxidation   and   Reduction. — Any  substance  which  like 
hydrogen  has  the  power  to  abstract  oxygen  from  com- 


THE   OXYHYDROGEN  BLOWPIPE.  65 

pounds  containing  it,  is  called  a  reducing  agent.  The 
process  of  abstracting  oxygen  from  a  compound  is  called 
reduction.  Reduction  and  oxidation  are  therefore  comple- 
mentary processes.  We  shall  hereafter  become  acquainted 
with  a  number  of  important  and  interesting  reducing 
processes. 

The  Oxyhydrogen  Blowpipe. — The  heat  evolved  when 
hydrogen  combines  with  oxygen  is  very  great,  and  it  is 
utilized  for  various  purposes.  To  burn  hydrogen  in  the 
air  is,  as  we  have"~s5en,  a  simple  matter,  but  to  burn  it  in 
oxygen  requires  a  special  apparatus  to  prevent  the  mixing 
of  the  gases  before  they  reach  the  end  of  the  tube  where 
the  combustion  takes  place.  The  oxyhydrogen  lloivpipe 
answers  this  purpose.  It  is  simply  a  tube  with  a  smaller 
tube  passing  through  it,  as  shown  in  Fig.  24. 


Fro.  24. 

The  oxygen  is  admitted  through  #,  and  the  hydrogen 
through  I.  It  will  be  seen  that  they  come  together  only 
at  the  end  of  the  tube.  The  hydrogen  is  first  passed 
through  and  lighted;  then  the  oxygen  is  passed  through 
slowly,  the  pressure  being  increased  until  the  flame 
appears  thin  and  straight.  It  gives  very  little  light,  but  is 
intensely  hot. 

EXPERIMENT  47.— Hold  in  the  flame  of  the  oxykydrogen  blow- 
pipe successively  a  piece  of  iron  wire,  a  piece  of  a  steel  watch- 
spring,  a  piece  of  copper  wire,  a  piece  of  zinc,  a  piece  of  platinum 
wire. 

Platinum  vessels  are  used  for  many  purposes,  particu- 
larly for  chemical  operations.  The  vessels  are  made  from 


66  INTRODUCTION   TO   CHEMISTRY. 

molten  platinum,  the  metal  being  melted  by  means  of  the 
oxyhydrogen  blowpipe. 

The  Lime  Light. — When  this  flame  is  allowed  to  play 
upon  some  substance  which  it  cannot  melt  nor  burn  up, 
the  substance  becomes  heated  so  high  that  it  gives  off  an 
intense  light.  The  substance  commonly  used  is  quicklime. 
Hence  the  light  is  often  called  the  lime  light.  It  is  also 
known  as  the  Drummond  light. 

EXPERIMENT  48. — Cut  a  piece  of  lime  of  convenient  size  and 
shape,  say  25  mm.  (1  inch)  long  by  20  mm.  (f  inch)  wide,  and 
the  same  thickness.  Fix  it  in  position  so  that  the  flame  of  the 
oxyhydrogen  blowpipe  will  play  upon  it.  The  light  is  very  bright, 
but  by  no  means  as  intense  as  the  electric  light. 

Natural  Waters. — The  purest  water  found  in  nature  is 
rain-water,  particularly  that  which  falls  after  it  has  rained 
for  some  time.  That  which  first  falls  always  contains 
impurities  from  the  air.  As  soon  as  the  rain-water  comes 
in  contact  with  the  earth,  and  begins  its  course  towards 
the  ocean,  it  begins  to  take  up  various  substances,  accord- 
ing to  the  character  of  the  soil  with  which  it  comes  in 
contact.  Mountain  streams  that  flow  over  rocky  beds, 
particularly  over  beds  of  sandstone,  which  is  very  insoluble, 
contain  exceptionally  pure  water.  Streams  that  flow 
over  limestone  dissolve  some  of  the  stone,  and  the  water 
becomes  "hard."  The  many  varieties  of  mineral  springs 
have  their  origin  in  the  presence  in  the  earth  of  certain 
substances  which  are  soluble  in  water.  Common  salt 
occurs  in  large  quantities  in  different  parts  of  the  earth. 
As  it  is  easily  soluble  in  water,  many  streams  contain  it; 
and  as  all  the  streams  find  their  way  into  the  ocean,  we  see 
one  reason  why  the  water  of  the  ocean  should  be  salt.  As 
streams  approach  the  habitations  of  man  they  are  subjected 
to  a  serious  cause  of  contamination.  The  drainage  from 
the  neighborhood  of  human  dwellings  is  very  apt  to  find 


TESTING   OF  DRINKING-WATER.  67 

its  way  into  a  near  stream.  This  condition  of  things  is 
most  strikingly  illustrated  by  the  case  of  a  large  town 
situated  on  the  banks  of  a  river.  It  frequently  happens 
that  the  water  of  the  river  is  used  for  drinking  purposes, 
and  it  also  frequently  happens  that  the  water  is  contami- 
nated by  drainage.  Water  when  once  contaminated  by 
drainage  tends  to  become  pure  again  by  contact  with  the 
air.  If  it  is  to  be  used  for  drinking  purposes,  however,  it 
is  not  well  to  rely  too  much  upon  this  process  of  purifica- 
tion. 

Testing  of  Drinking-water. — There  is  no  simple  process 
by  which  the  value  of  a  water  for  drinking  purposes  can 
be  determined  in  doubtful  cases.  Any  marked  odor, 
color,  or  taste  furnishes  good  grounds  for  suspicion.  But 
many  waters  that  are  inodorous,  colorless,  and  tasteless  are 
not  fit  for  use.  In  case  of  doubt  a  water  should  be  sub- 
mitted to  a  skilled  chemist.  Any  examination  made  by 
an  amateur  is  of  practically  no  value. 

Distillation  of  Water. — In  order  to  get  pure  water,  it 
must  be  distilled.  Distillation  consists  in  boiling  the 
water,  and  then  condensing  the  vapor  by  passing  it  through 
a  tube  which  is  kept  cool  by  surrounding  it  with  cold 
water.  A  simple  apparatus  for  the  purpose  is  that  illus- 
trated in  Fig.  25. 

The  water  to  be  distilled  is  placed  in  the  flask  A.  The 
flask  •  is  connected  by  means  of  a  bent  glass  tube  B  with 
the  long  tube  (7(7.  This  in  turn  is  surrounded  by  the 
larger  tube  or  jacket  D.  The  side  tube  E  is  connected 
with  a  faucet  by  means  of  the  rubber  tube  G.  The  water 
is  allowed  to  flow  slowly  into  the  jacket  and  out  at  F, 
whence  it  passes  through  the  rubber  tube  H  to  the  sink. 
When  the  water  in  A  is  boiled,  the  vapor  passes  into  the 
tube  CO.  Here  it  is  cooled  down,  and  takes  tie  form  of 


68 


INTRODUCTION    TO   CHEMISTRY. 


liquid,  which  runs  down  and  collects  in  the  flask  A",  which 
is  called  the  receiver. 

EXPERIMENT  49. — Dissolve  some  copper  sulphate,  or  other  col- 
ored substance,  in  a  litre  of  water,  and  distil  the  water. 


Properties  of  Water. — Pure  water  is  tasteless  and  in- 
odorous. In  thin  layers  it  is  colorless,  but  in  thick  layers 
it  is  blue.  This  has  been  shown  in  the  laboratory  by 
filling  a  long  tube  with  distilled  water.  When  looked 
through  it  appears  blue.  The  beautiful  blue  color  of  the 
water  of  some  lakes  is  the  natural  color  of  pure  water. 

On  cooling,  water  contracts  until  it  reaches  the  tem- 
perature 4°.  At  this  point  it  has  its  maximum  density. 
When  cooled  below  4°  it  expands,  and  the  specific  gravity 
of  ice  is  somewhat  less  than  that  of  water.  Hence  ice 
floats  on  water. 

Water  as  a  Solvent. — It  is  known  that  many  solids, 
liquids,  and  gases  when  brought  into  water  disappear  and 
form  colorless  liquids  which  look  like  water.  Some  give 
colored  liquids  of  the  same  color  as  the  substance  dissolved, 
and  others  give  liquids  which  have  colors  quite  different 


SOLUTIONS  AND   CHEMICAL   COMPOUNDS.  69 

from  the  dissolved  substances.  On  the  other  hand  there 
are  many  substances  that  do  not  dissolve  in  water.  If  a 
very  small  quantity  of  substance  is  dissolved  in  a  large 
quantity  of  water,  and  the  solution  thoroughly  stirred,  the 
dissolved  substance  is  uniformly  distributed  throughout 
the  liquid,  as  can  be  shown  by  refined  chemical  methods. 
That  the  dissolved  substance  is  everywhere  present  in  the 
solution  can  be  shown,  further,  by  the  aid  of  certain  dye- 
stuffs,  as,  for  example,  magenta.  A  drop  of  a  concen- 
trated solution  of  this  substance  brought  into  many  gallons 
of  water  imparts  a  distinct  color  to  all  parts  of  the  liquid. 
-An  experiment  of  this  kind  gives  some  idea  of  the  extent 
to  which  the  subdivision  of  matter  can  be  carried.  For  it 
is  evident  that  in  each  drop  of  the  dilute  solution  some  of 
the  coloring  matter  must  be  contained,  though  the  quantity 
must  be  what  we  should  call  infinitesimal.  While  there 
seems  to  be  no  limit  to  the  extent  to  which  a  solution  can 
be  diluted,  and  still  retain  the  dissolved  substance  uniformly 
distributed  through  its  mass,  there  is  a  limit  to  the  amount 
of  every  substance  that  can  be  brought  into  solution,  and 
this  varies  with  the  temperature,  and,  in  the  case  of  gases, 
with  the  pressure.  Some  substances  are  easily  soluble; 
others  are  difficultly  soluble.  When  the  solutions  are 
boiled  the  water  simply  passes  off  and  leaves  the  dissolved 
substance  behind,  if  it  is  a  non-volatile  solid.  If,  however, 
the  substance  in  solution  is  a  liquid  a  partial  separation 
will  take  place,  the  extent  of  the  separation  depending 
largely  upon  the  difference  between  the  boiling-points  of 
the  water  and  the  other  liquid.  If,  finally,  the  substance 
in  solution  is  a  gas,  it  generally  passes  off  when  the  solu- 
tion is  heated,  though  in  some  cases  water  is  given  off, 
leaving  the  gas  in  solution. 

Solutions  and  Chemical  Compounds. — Solutions,  in  gen- 
eral,, seem  to  differ  from  true  chemical  compounds  in  some 


70  INTRODUCTION   TO   CHEMISTRY. 

important  particulars,  and  also  from  mere  mechanical 
mixtures.  Definiteness  of  composition  is  a  common  char- 
acteristic of  .chemical  compounds,  but  solutions  have  no 
definite  composition.  Any  quantity  of  a  substance,  from 
the  minutest  particle  to  a  certain  fixed  quantity,  can  be 
dissolved,  and  the  solution  formed  is  in  each  case  uniform 
and  appears  to  be  a  perfect  solution.  The  subject  of  solu- 
tion is  at  present  under  investigation,  and  much  light  has 
been  thrown  upon  it. 

Solution  as  an  Aid  to  Chemical  Action. — When  it  is 
desired  to  secure  the  chemical  action  of  one  solid  substance 
upon  another  it  is  frequently  found  advantageous  to  bring 
them  together  in  solution.  The  full  explanation  of  this 
remains  yet  to  be  given,  but  it  appears  highly  probable  that 
when  a  substance  is  dissolved  in  water  some  deep-seated 
change  takes  place  in  it,  and  that  this  is  one  of  the  prin- 
cipal reasons  why  substances  in  solution  act  upon  each 
other  so  readily.  This  subject  will  be  discussed  farther 
on. 

Ozone. — When  electric  sparks  are  passed  for  a  time 
through  oxygen  the  gas  undergoes  a  remarkable  change. 
It  acquires  a  strong  odor,  and  is  much  more  active  than 
under  ordinary  circumstances.  The  odor  of  the  gas  is 
observed  in  the  neighborhood  of  an  electric  machine  in 
action,  and  is  said  to  be  noticed  during  thunder-storms. 
The  substance  which  has  the  odor  is  ozone.  It  is  formed 
in  a  number  of  chemical  reactions,  as  when  phosphorus 
acts  on  the  air  in  the  presence  of  water.  By  cold  and 
pressure  it  has  been  changed  to  a  dark-blue  liquid. 

When  a  certain  volume  of  oxygen  is  converted  into  ozone 
the  volume  of  gas  is  decreased  from  three  to  two. 

By  heating  ozone  above  300°  it  is  converted  into  ordinary 
oxygen,  and  its  volume  is  increased  from  two  to  three. 


HYDROGEN  DIOXIDE.  71 

It  is  clear  that  the  element  oxygen  can  be  converted  into 
something  else  without  the  addition  of  any  substance  to 
it.  This  might  lead  us  to  conclude  that  oxygen  is  not  an 
element.  But  the  substance  formed  from  it  has  exactly 
the  same  weight  and  can  be  changed  back  again  to  oxygen 
without  any  substance  being  added  to  it  or  taken  from  it. 
It  follows  that  the  change  must  take  place  within  the 
oxygen  itself.  The  commonly  accepted  explanation  of  the 
relation  between  oxygen  and  ozone  will  be  given  later. 

Ozone  is  present  in  small  quantity  in  the  air. 

Hydrogen  Dioxide. — Besides  water,  hydrogen  and  oxygen 
form  a  second  compound  with  each  other.  This  is 
hydrogen  dioxide.  It  is  prepared  by  treating  barium 
dioxide  with  sulphuric  acid.  The  reaction  that  takes 
place  will  be  explained  under  barium  dioxide. 

Hydrogen  dioxide  is  a  liquid  that  breaks  up  readily  into 
water  and  oxygen.  The  ease  with  which  it  gives  up  oxygen 
makes  it  a  good  oxidizing  agent.  It  is  now  manufactured 
on  the  large  scale. 

Analysis  has  shown  that  hydrogen  dioxide  contains 
relatively  twice  as  much  oxygen  as  water  does.  While,  in 
the  latter  substance,  hydrogen  and  oxygen  are  combined 
in  the  proportion  of  one  part  by  weight  of  hydrogen  to 
eight  parts  by  weight  of  oxygen,  in  hydrogen  dioxide  there 
are  sixteen  parts  by  weight  of  oxygen  to  one  part  by  weight 
of  hydrogen. 

Summary. — We  have  thus  learned  that  (1)  water  can  be 
decomposed  into  hydrogen  and  oxygen  by  means  of  an 
electric  current;  (2)  the  gases  are  obtained  in  the  propor- 
tion of  eight  parts  by  weight  of  oxygen  to  one  part  by 
weight  of  hydrogen,  or  one  volume  of  oxygen  to  two 
volumes  of  hydrogen ;  (3)  when  hydrogen  is  burned  water 
is  formed;  (4)  when  hydrogen  and  oxygen  are  mixed 


72  INTRODUCTION   TO  CHEMISTRY. 

together  they  do  not  combine  under  ordinary  circum- 
stances; (5)  when  a  spark  or  flame  is  brought  in  contact 
with  the  mixture  violent  action  takes  place  accompanied 
by  explosion;  (6)  the  action  is  occasioned  by  the  chemical 
combination  of  the  two  gases;  (7)  they  combine  in  the 
same  proportions  as  those  in  which  they  are  obtained  from 
water  by  the  action  of  the  electric  current;  (8)  water  can 
be  made  by  passing  hydrogen  over  heated  copper  oxide ; 
(9)  by  weighing  the  copper  oxide  before  and  after  the  ex- 
periment, and  determining  the  weight  of  the  water 
formed,  oxygen  is  found  to  form  eight  ninths  of  water. 

Comparison  of  Hydrogen  and  Oxygen. — Hydrogen  and 
oxygen  are  different  forms  of  matter,  just  as  heat  and 
motion  are  different  forms  of  energy.  Heat  can  be  con- 
verted into  motion,  and  motion  into  heat,  but  one  element 
cannot  by  any  means  known  to  us  be  converted  into 
another.  They  are  apparently  entirely  independent  of 
each  other.  The  question  will  therefore  suggest  itself, 
whether,  in  spite  of  their  apparent  independence,  there  is 
not  some  relation  between  the  different  elements  which 
reveals  itself  by  similarity  in  properties.  It  will  be  found 
that  the  elements  can  be  divided  into  groups  or  families 
according  to  their  properties.  There  are  some  elements, 
for  example,  which  in  their  chemical  conduct  resemble 
oxygen  markedly.  These  elements  make  up  the  oxygen 
family.  So  far  as  hydrogen  is  concerned,  however,  it 
stands  by  itself.  There  is  no  other  element  that  conducts 
itself  like  it.  If  we  compare  it  with  oxygen,  we  find  very 
few  facts  that  indicate  any  analogy  between  the  two  ele- 
ments. In  their  physical  properties  they  are,  to  be  sure, 
similar.  Both  are  transparent,  colorless,  inodorous  gases. 
On  the  other  hand,  oxygen  combines  readily  with  a  large 
number  of  substances  with  which  hydrogen  does  not  com- 
bine. Oxygen,  as  we  have  seen,  combines  easily  with 


COMPARISON  OF  HYDROGEN  AND  OXYGEN.  73 

carbon,  sulphur,  phosphorus,  and  iron.  It  is  a  difficult 
matter  to  get  any  of  these  elements  to  combine  directly 
with  hydrogen.  Further,  substances  that  combine  readily 
with  hydrogen  do  not  combine  readily  with  oxygen.  The 
two  elements  exhibit  opposite  chemical  properties.  What 
one  can  do  the  other  cannot  do.  This  oppositeness  of 
properties  is  favorable  to  combination;  for  not  only  do 
hydrogen  and  oxygen,  with  their  opposite  properties, 
combine  with  great  ease  under  the  proper  conditions,  but, 
as  we  shall  see  later,  it  is  a  rule  that  elements  of  like 
properties  do  not  readily  combine  with  one  another,  while 
elements  of  unlike  properties  do  readily  combine  with  one 
another. 


V 


CHAPTER  V. 

LAWS  OF  CHEMICAL  COMBINATION.— COMBINING 
WEIGHTS.— ATOMIC  WEIGHTS.— CHEMICAL  EQUA- 
TIONS. 


Law  of  the  Indestructibility  of  Matter. — The  earlier 
chemists  do  not  appear  to  have  been  very  strongly  im- 
pressed by  the  importance  of  the  weight  of  substances. 
They  seem  tacitly  to  have  held  that  matter  can  be  destroyed 
or  brought  into  being.  The  work  of  Lavoisier,  however, 
in  the  last  part  of  the  last  century,  showed  that  whenever 
matter  is  apparently  destroyed,  it  continues  to  exist  in 
some  other  form.  If  it  were  possible  to  annihilate  matter 
or  to  call  it  into  being  at  will,  it  would  be  of  little  or  no 
scientific  value  to  weigh  things.  Innumerable  experiments 
performed  since  Lavoisier's  time  have  confirmed  the  view 
that  matter  is  indestructible.  The  first  fundamental  law 
bearing  upon  the  changes  in  composition  which  the  differ- 
ent forms  of  matter  undergo  is  -the  law  of  the  indestructi- 
bility of  matter,  or  the  law  of  the  conservation  of  mass. 
While  it  is  perhaps  impossible  to  conceive  that  this  great 
law  should  not  be  true,  it  must  not  be  forgotten  that  the 
only  way  by  which  its  truth  could  be  established  was  by 
experiment.  The  law  may  be  stated  thus  :. 

Whenever  a  change  in  the  composition  of  a  substance 
takes  place  the  amount  of  matter  after  the  change  is  the 
same  as  before  the  change. 

Assuming  that  this  law  has  always  held  good,  it  follows 
that  the  amount  of  matter  in  the  universe  is  the  same  to- 

74 


LAW  OF  THE  CONSERVATION  OF  ENERGY.  75 

day  as  it  has  been  from  the  beginning.  Transformations 
are  constantly  taking  place,  but  these  involve  no  increase 
nor  decrease  in  the  total  amount  of  matter. 

Law  of  the  Conservation  of  Energy, — Just  as  matter  is 
neither  created  nor  destroyed,  so  it  has  been  shown  that 
the  total  amount  of  energy  is  unchangeable.  One  of  the 
greatest  discoveries  in  science  is  that  one  form  of  energy 
can  be  transformed  into  others,  and  that  in  these  trans- 
formations nothing  is  lost.  It  is  now  known  that  for  a 
certain  amount  of  heat  a  certain  amount  of  motion  can  be 
obtained,  and  that  for  a  certain  amount  of  motion  a 
certain  amount  of  heat  can  be  obtained.  It  is  known  that 
a  similar  definite  relation  exists  between  heat  and  electrical 
energy.  It  is  known  that  a  definite  amount  of  heat  is 
obtained  by  burning  a  definite  amount  of  a  given  sub- 
stance, and  it  is  known  also  that  a  definite  amount  of  heat 
can  cause  a  definite  amount  of  chemical  change.  Investi- 
gation has  shown  that  all  the  different  forms  of  energy  are 
convertible  one  into  the  other  without  loss.  This  great 
fact  is  known  as  the  law  of  the  conservation  of  energy. 
Transformations  of  energy  are  constantly  taking  place,  as 
.  transformations  of  many  varieties  of  matter  are,  but  the 
total  amount  in  each  case  remains  the  same. 

Law  of  Definite  Proportions. — Under  oxygen  the  fact 
was  mentioned  that  magnesium  and  oxygen  combine  with 
each  other  in  definite  proportions.  This  raises  the  question 
as  to  the  proportion  by  weight  in  which  other  elements 
combine  with  one  another.  A  magnet  of  a  certain 
strength  can  support  a  piece  of  iron  of  a  certain  weight. 
But  it  will  also  support  any  piece  of  iron  weighing  les?. 
It  shows  no  preference  for  certain  weights  of  iron.  So, 
also,  the  earth  attracts  all  bodies,  light  or  heavy,  showirg 
no  preference  for  certain  weights.  When  substances  act 


76  INTRODUCTION    TO   CHEMISTRY. 

upon  one  another  chemically,  however,  it  is  found  that  a 
certain  weight  of  one  will  combine  with  a  definite  weight 
of  another,  and  only  with  this  weight — no  more  and  no 
less.  Take,  for  example,  the  case  of  iron  and  sulphur. 
If  equal  weights  of  these  elements  are  mixed  and  caused 
to  act  chemically  by  the  aid  of  heat,  it  will  be  found  that 
some  of  the  sulphur  is  left  in  the  uncombined  state  after 
the  action  is  over.  If  twice  as  much  iron  as  sulphur  is 
taken,  then,  after  the  action,  some  iron  is  left.  A  large 
number  of  experiments  have  shown  that  when  the  two 
elements  are  mixed  in  the  proportion  of  7  parts  by  weight 
of  iron  to  4  parts  of  sulphur  the  action  is  perfect,  neither 
iron  nor  sulphur  being  left. 

An  extensive  examination  has  shown  conclusively  that 
any  given  chemical  compound  always  contains  the  same 
elements  in  exactly  the  same  proportions.  The  compound 
of  sulphur  and  iron  always  contains  exactly  36.36  per  cent 
of  sulphur  and  63.64  per  cent  of  iron.  The  compound  of 
magnesium  and  oxygen  always  contains  exactly  60  per  cent 
of  magnesium  and  40  per  cent  of  oxygen,  and  so  on 
throughout  the  list  of  chemical  elements.  These  facts 
were  discovered  by  the  united  efforts  of  a  large  number  of 
chemists  continued  through  many  years.  They  are  of 
very  great  importance.  They  are  summed  up  in  the 
general  statement: 

Chemical  combination  always  takes  place  between  definite 
masses  of  substances. 

This  is  known  as  the  law  of  definite  proportions.  It  is 
simply  a  statement  of  what  we  have  every  reason  to  believe 
to  be  the  truth.  Every  fact  known  to  us  in  regard  to 
chemical  combination  is  in  accordance  with  this  general 
statement.  It  expresses  what  we  learn  by  a  study  of 
chemical  facts.  It  must  be  borne  in  mind  that  this  law, 
as  well  as  other  laws  governing  natural  phenomena,  can 
never  be  proved  to  be  absolutely  true,  for  the  reason  that 


LAW  OF  MULTIPLE  PROPORTIONS.  77 

we  cannot  examine  every  case  to  which  the  law  applies. 
But  if,  after  examining  a  very  large  number  of  cases,  we 
find  that  the  law  always  holds  true,  we  are  justified  in 
concluding  that  it  is  true  of  all  cases.  When  we  say  that 
all  bodies  attract  one  another,  do  we  know  this  to  be 
absolutely  true  ?  Certainly  not.  But  we  do  know  that, 
so  far  as  those  bodies  are  concerned  which  come  under  our 
observation,  the  statement  is  true,  and  we  therefore  have 
every  reason  to  believe  that  it  is  true  of  all  bodies. 

Law  of  Multiple  Proportions. — It  does  not  require  a  very 
extended  study  of  chemical  phenomena  to  show  that  from 
the  same  elements  it  is  possible  in  many  cases  to  get  more 
than  one  product.  Thus,  iron  and  sulphur  form  three 
distinct  compounds  with  each  other.  Tin  combines  with 
oxygen  in  two  proportions.  The  elements  potassium, 
chlorine,  and  oxygen  combine  in  four  different  ways, 
forming  four  distinct  products.  Nitrogen  and  oxygen  form 
five  products.  In  the  early  part  of  this  century  the 
English  chemist  Dalton  by  a  study  of  cases  like  those 
mentioned  was  led  to  the  discovery  of  another  great  law  of 
chemistry,  known  as  the  law  of  multiple  proportions. 
Many  substances  had  been  analyzed  before  his  time,  and 
the  percentage  of  the  constituents  determined  with  a  fair 
degree  of  accuracy.  He  examined  first  two  gases,  both  of 
whch  consist  of  carbon  and  hydrogen.  He  determined  the 
percentages  of  their  constituents,  and  found  them  to  be 
as  follows: 

Olefiant  gas,  85.7$  carbon  and  14.3$  hydrogen; 
Marsh-gas,  75.0$  carbon  and  25.0$  hydrogen. 

On  comparing  these  numbers  he  found  that  the  ratio  of 
carbon  to  hydrogen  in  olefiant  gas  is  as  6  :  1;  whereas  in 
marsh-gas  it  is  as  3  :  1  or  6  :  2.  The  mass  of  hydrogen, 


7$  INTRODUCTION    TO   CHEMISTRY. 

combined  with  a  given  mass  of  carbon,  is  exactly  twice  as 
great  in  the  one  case  as  in  the  other. 

There  are,  further,  two  compounds  of  carbon  and 
oxygen,  and  in  analyzing  these  the  following  figures  were 
obtained : 

Carbon  monoxide,  42.86$  carbon  and  57.14$  oxygen; 
Carbon  dioxide,  27.27$  carbon  and  72.73$  oxygen. 

But    42.86  :  57.14  ::  3  :  4,     and    27.27  :  72,73  : :  3  :  8. 

The  mass  of  oxygen  combined  with  a  given  mass  of 
carbon  in  carbon  dioxide  is  exactly  twice  as  great  as  the 
mass  of  oxygen  combined  with  the  same  mass  of  carbon  in 
carbon  monoxide.  These  facts  and  other  similar  ones  led 
to  the  discovery  of  the  law  of  multiple  proportions,  which 
may  be  stated  thus : 

If  two  elements  form  several  compounds  with  each  other, 
the  masses  of  one  that  combine  with  a  fixed  mass  of  the  other 
bear  a  simple  ratio  to  one  another. 

The  three  compounds  of  iron  and  sulphur  may  serve  as 
further  illustrations.  In  one  of  them,  approximately 
7  parts  by  weight  of  iron  are  in  combination  with  4  parts 
of  sulphur;  in  a  second,  7  parts  of  iron  are  in  combination 
with  6  parts  of  sulphur;  and  in  the  third,  7  of  iron  are  in 
combination  with  8  of  sulphur.  The  figures  4,  6,  and  8 
plainly  bear  a  simple  ratio  to  one  another.  The  five  com- 
pounds of  the  element  nitrogen  with  oxygen  contain 
7  parts  by  weight  of  nitrogen  and  4,  8,  12,  16,  and  20 
parts  by  weight  of  oxygen  respectively,  which  figures 
plainly  bear  a  simple  relation  to  one  another,  viz.,  1:2: 
3:4:5. 

The  law  of  multiple  proportions,  like  the  law  of  definite 
proportions,  is  simply  a  statement  in  accordance  with  what 
has  been  found  true  by  experiment.  Although  discovered 
by  Dalton  at  the  beginning  of  this  century  and  put  forward 
upon  what  appears  now  to  be  a  slight  basis  of  facts,  all 


COMBINING   WEIGHTS  OF   THE  ELEMENTS.  79 

work  since  that  time  has  confirmed  it,  and  it  forms  to-day 
one  of  the  corner-stones  of  the  science  of  chemistry. 

Combining  Weights  of  the  Elements. — A  careful  study 
of  the  figures  representing  the  composition  of  chemical 
compounds  reveals  a  remarkable  fact  regarding  the  relative 
quantities  of  one  and  the  same  element  that  enter  into 
combination  with  different  elements.  The  proportions  by 
weight  in  which  some  of  the  elements  combine  chemically 
with  one  another  are  given  in  the  following  table : 

1  part  Hydrogen  combines  with       35.18  parts  Chlorine. 


1    "            "                "                       79.36 

Bromine. 

1    "            "                "           "         125.9 

Iodine. 

35.18  pa 
79.36 

rts  Chlorine    com 
Bromine 

sine  w 

ith    38.86 
38.86 

Potassium. 

125.9 

Iodine 

38.86 

« 

"15.88 
15.88 
15.88 

Oxygen 
« 

64.9 
24.18 
39.7 

Zinc, 
Magnesium. 
Calcium. 

15.88 

<  < 

136.4 

Barium. 

64.9 

24.18 
39.7 

Zinc 
Magnesium 
Calcium 

31.83 
31.83 
31.83 

Sulphur. 
« 

« 

136.4 

Barium 

'. 

31.83 

M 

It  will  be  seen  that  the  figures  that  express  the  relative 
weights  of  chlorine,  bromine,  and  iodine  that  combine 
with  1  part  of  hydrogen  also  express  the  relative  weights 
of  these  elements  that  combine  with  38.86  parts  of  potas- 
sium. So  also  the  figures  that  express  the  relative  weights 
of  zinc,  magnesium,  calcium,  and  barium  that  combine 
with  15.88  parts  of  oxygen  express  the  relative  weights 
of  these  elements  that  combine  with  31.83  parts  of  sul- 
phur. Now  an  examination  of  all  compounds  has  shown 
that  hydrogen  enters  into  combination  with  the  other 
elements  in  the  smallest  proportions;  and  this  element  is 
therefore  taken  as  unity  in  stating  the  relative  weights  of 


So  INTRODUCTION   TO   CHEMISTRY. 

the  other  elements  that  enter  into  combination.  That 
weight  of  another  element  that  combines  with  1  part  by 
weight  of  hydrogen  may  be  called  its  combining  weight. 
Thus,  according  to  this,  the  combining  weights  of  chlorine, 
bromine,  and  iodine  are  respectively  35.18,  70.30,  and 
125.9.  Similarly,  38.86  is  the  combining. weight  of  potas- 
sium, as  it  expresses  the  weight  of  potassium  that  combines 
with  the  above  weights  of  chlorine,  bromine,  and  iodine. 
For  every  element  a  number  can  be  selected  such  that  the 
proportions  by  weight  in  which  the  element  enters  into 
combination  with  others  can  be  conveniently  expressed  by 
this  number  or  by  a  simple  multiple  of  it.  These  numbers 
are  called  the  combining  weights. 

Hypothesis  and  Theory. — The  laws  presented  in  this 
chapter  are  condensed  statements  that  sum  up  what  has 
been  found  true  in  all  cases  examined.  They  are  state- 
ments of  facts  discovered  by  experiment. 

When  we  have  established  a  law  by  means  of  experi- 
ments, the  next  thing  in  order  is  to  to  imagine  a  cause. 
We  try  to  imagine  a  condition  of  things  which,  if  it  existed, 
would  lead  to  the  results  discovered.  If  we  succeed  in 
imagining  such  a  condition  of  things,  this  leads  to  an 
hypothesis.  If,  now,  we  test  this  hypothesis  in  every  way 
that  suggests  itself,  and  find  that  all  facts  discovered  are 
in  accordance  with  it,  we  then  call  it  a  theory.  An 
hypothesis  is  a  guess  in  regard  to  the  cause  of  certain 
phenomena.  A  theory  is  an  hypothesis  that  has  been 
thoroughly  tested,  and  is  applicable  to  a  large  number  of 
related  phenomena. 

Hypotheses  and  theories  are  of  great  value  to  science, 
if  founded  upon  a  thorough  knowledge  of  the  facts  to 
which  they  relate.  They  become  dangerous  when  used  by 
those  who  are  not  familiar  with  the  facts.  Those  whose 
minds  have  not  been  properly  trained  are  apt  to  be  given 


THE  ATOMIC   THEORY.  81 

to  unprofitable  speculation.  The  student  who  has  not 
received  a  thorough  scientific  training  should  remember 
that  theories  and  hypotheses,  to  be  of  value,  must  be  sug- 
gested, not  by  a  superficial  but  by  a  thorough  knowledge 
of  facts. 

With  these  words  of  warning  and  of  explanation  in 
regard  to  the  relation  existing  between  the  fact,  the  law, 
the  hypothesis,  and  the  theory,  we  may  proceed  to  consider 
briefly  a  theory  concerning  the  constitution  of  matter 
which  grew  out  of  the  discovery  of  the  laws  of  definite  and 
multiple  proportions. 

The  Atomic  Theory. — If  we  consider  any  simple  form  of 
matter  or  element,  such  as  iron,  it  is  clear  that  there  are 
two  views  that  may  be  held  regarding  the  way  the  sub- 
stance is  made  up.  We  know  that  we  can  subdivide  every 
piece  of  iron  we  can  see,  no  matter  how  small  it  may  be ; 
and  though  after  a  time  the  particles  might  become  so 
small  that  we  could  no  longer  subdivide  them,  still  we  can 
imagine  that  by  more  refined  methods  the  process  of  sub- 
division might  be  continued  without  end.  If  we  believe 
that  such  infinite  subdivision  is  possible,  we  hold  the 
hypothesis  that  matter  is  infinitely  divisible.  We  cannot 
prove  this — we  can  only  speculate  in  regard  to  it.  But 
we  may  also  conceive  that  after  the  process  of  subdivision 
has  been  carried  on  for  a  time,  until  very  minute  particles 
have  been  obtained,  a  limit  can  be  reached  beyond  which 
the  process  of  subdivision  cannot  be  carried.  If  we 
believe  this,  we  hold  the  hypothesis  that  matter  is  riot 
infinitely  divisible,  or  that  matter  consists  of  indivisible 
particles.  These  particles  may  be  called  atoms  (from  the 
Greek  aropos,  which  signifies  simply  indivisible).  Both 
of  these  hypotheses  have  been  held  for  ages.  But  the  dis- 
cussion in  regard  to  the  relative  merits  of  the  two  views 
was  at  first  not  much  more  profitable  than  it  would  be  if 


82  INTRODUCTION   TO  CHEMISTRY. 

carried  on  between  two  students  who  are  in  the  earJy 
stages  of  their  study  of  the  facts. 

When  the  laws  of  definite  and  multiple  proportions  AT  ere 
discovered  by  Dalton,  he  saw  that  the  conception  that 
matter  is  made  up  of  indivisible  particles  or  atoms  might 
have  some  connection  with  the  laws.  If  each  element  is 
made  up  of  atoms,  the  most  probable  view  is  that  every 
atom  of  any  particular  element  is  exactly  like  every  other 
atom  of  that  element.  Among  the  properties  possessed 
by  these  atoms  must  be  weight.  It  is  probable  that  the 
atoms  of  different  elements  have  different  weights.  Sup- 
pose now  that,  when  chemical  combination  takes  place 
between  two  elements,  the  action  takes  place  between  these 
atoms,  so  that  one  atom  of  the  one  element  combines  with 
one  of  the  other,  and  so  on  through  the  mass.  If  there 
were  present  in  one  mass  exactly  as  many  atoms  as  in  the 
other,  both  elements  would  enter  completely  into  combina- 
tion— nothing  would  be  left  over.  But  if  there  were  a 
larger  number  of  atoms  of  one  element  than  of  the  other, 
then,  of  the  element  of  which  the  larger  number  of  atoms 
is  present,  some  would  be  left  over  after  the  action  is  com- 
plete. Suppose,  further,  that  the  weights  of  the  atoms  of 
two  elements  are  to  each  other  as  1  : 10.  Then,  if,  when 
these  two  elements  are  brought  together,  they  combine  in 
the  proportion  of  one  atom  of  one  to  one  atom  of  the  other, 
the  resulting  compound  would  contain  the  elements  in  the 
proportion  of  one  part  by  weight  of  one  to  ten  parts  by 
weight  of  the  other.  Or  if,  on  analyzing  a  compound  of 
two  elements,  we  find  that  it  contains  one  part  by  weight 
of  one  to  ten  parts  by  weight  of  the  other,  we  should  con- 
clude that  the  weights  of  the  atoms  of  the  two  elements 
bear  to  each  other  the  ratio  1 : 10. 

If  matter  consists  of  atoms,  and  chemical  action  takes 
place  between  these  atoms,  we  can  understand  why  chem- 
ical action  takes  place  between  definite  weights  of  sub- 


ATOMIC   WEIGHTS.  83 

stances;  in  other  words,  we  see  a  probable  reason  for  the 
law  of  definite  proportions.  As  the  atoms  are  supposed 
to  be  indivisible,  if  two  elements  combine  in  more  than 
one  proportion  with  each  other,  they  must  do  so  in  the 
proportion  of  one  atom  of  one  to  two  atoms  of  the  other, 
or  one  to  three,  or  two  to  three,  or  in  some  other  way  that 
does  not  involve  the  breaking-up  of  the  atoms.  If,  for 
example,  two  elements,  the  weights  of  whose  atoms  are  as 
1  to  10,  combine  in  the  proportion  of  one  atom  of  one  to 
one  atom  of  the  other,  the  resulting  compound  will  con- 
tain the  elements  in  the  proportion  of  one  part  by  weight 
of  one  to  ten  parts  by  weight  of  the  other  element.  If 
the  same  elements  combine  in  the  proportion  of  one  atom 
of  the  first  to  two  atoms  of  the  other,  then  the  resulting 
compound  will  contain  the  elements  in  the  proportion  of 
one  part  by  weight  of  one  to  twenty  parts  by  weight  of 
the  other,  and  so  on.  It  will  thus  be  seen  that  if  two 
elements  combine  in  more  than  one  proportion  with  each 
other,  and  the  view  that  matter  consists  of  atoms  of  definite 
weight,  and  that  chemical  action  takes  place  between  these 
atoms,  is  correct,  then  it  follows  that  the  elements  must 
combine  in  accordance  with  the  law  of  multiple  propor- 
tions. 

Atomic  Weights. — A  thorough  study  of  the  facts  has 
shown  that  the  atomic  theory,  as  suggested  by  Dalton,  is 
the  simplest  conception  that  can  be  formed  in  regard  to 
the  constitution  of  matter  which  will  satisfactorily  account 
for  the  laws  of  definite  and  multiple  proportions.  The 
weights  of  the  elements  which  have  thus  far  been  referred 
to  as  combining  weights  are,  in  accordance  with  the  theory, 
the  relative  weights  of  the  atoms,  or  the  atomic  weights. 
The  symbols  of  the  elements  represent  atoms  of  the 
elements.  Thus  H  represents  an  atom  of  hydrogen,  0  an 
atom  of  oxygen,  Cl  an  atom  of  chlorine,  etc.  The  com- 


84  INTRODUCTION   TO   CHEMISTRY. 

billing  weights,  found  by  analyzing  compounds  in  which 
these  elements  occur,  are  H  =  1,  0  =  15.88,  and  Cl  = 
35.18.  That  is  to  say,  by  means  of  these  figures  we  can 
always  represent  the  relative  weights  of  the  elements  found 
in  their  compounds.  Hydrochloric  acid,  for  example, 
contains  hydrogen  and  chlorine  in  the  proportion  of  1  part 
hydrogen  to  35.18  parts  chlorine.  Hence  it  is  believed 
that  the  weight  of  the  atom  of  hydrogen  is  to  that  of 
chlorine  as  1  to  35.18.  As"  hydrogen  enters  into  combina- 
tion in  smaller  proportion  than  any  other  element,  its 
combining  weight  or  atomic  weight  is  taken  as  the  unit, 
and  all  others  compared  with  it.  If  we  say  that  the 
atomic  weight  of  oxygen  is  15.88,  and  that  of  chlorine  is 
35.18,  we  mean  simply  that  the  atom  of  oxygen  is  15.88 
times  heavier  and  that  of  chlorine  35.18  times  heavier  than 
that  of  hydrogen.  We  might  take  any  other  standard,  but 
that  of  the  hydrogen  atom  is  the  simplest.  At  one  time 
the  atomic  weight  of  oxygen  was  taken  as  100,  and  then 
the  atomic  weights  of  the  other  elements  were  relatively 
larger. 

[PROBLEM.— If  we  call  the  atomic  weight  of  oxygen  100,  what 
would  those  of  hydrogen  and  chlorine  be  ?  The  atomic  weight  of 
hydrogen  being  accepted  as  1,  those  of  oxygen  and  chlorine  are 
15.88  and  35.18  respectively.] 

International  Atomic  Weights. — In  adopting  a  system 
of  atomic  weights  it  is  plainly  simplest  to  take  the  element 
with  the  lowest  atomic  weight  as  the  standard,  to  call  its 
atomic  weight  1,  and  then  give  all  other  atomic  weights 
in  terms  of  this  unit,  Our  present  system  started  this 
way.  At  first  the  atomic  weight  of  oxygen  was  found  to 
be  16.  For  many  years  atomic  weights  have  been  deter- 
mined by  the  analysis  of  oxygen  compounds,  and  the 
results  have  been  stated  on  the  assumption  that  the  atomic 
weight  of  oxygen  is  16.  It  has,  however,  been  shown  that 
the  atomic  weight  of  oxygen  is  not  16  but  15.88,  and  it  is 


HOW   THE  ATOMIC   W 'EIGHTS  ARE  DETERMINED.     85 

therefore  necessary  either  to  change  all  those  atomic 
weights  that  are  based  on  the  assumption  that  it  is  16.  or 
to  change  the  atomic  weight  of  hydrogen  and  leave  the 
others  unchanged.  A  majority  of  the  chemists  of  the 
world  have  agreed  to  change  the  atomic  weight  of  hy- 
drogen to  accord  with  the  atomic  weight  16  for  oxygen. 
It  becomes  accordingly  1.01.  This  system  is  illogical,  but 
it  seems,  on  the  whole,  less  objectionable  than  the  system 
based  upon  H  =  1,  which  carries  with  it  so  many  changes. 
The  atomic  weights  based  upon  0  =  16  and  H  =  1.01 
having  been  adopted  by  an.  International  Committee  of 
Chemists  are  called  "International  Atomic  Weights." 
These  are  used  in  this  book.  Both  sets  of  atomic  weights 
are  given  in  the  table  on  the  first  cover.  It  may  be  said, 
further,  that  for  ordinary  purposes  round  numbers  may  in 
most  cases  be  substituted  for  the  refined  atomic  weights. 
Thus  we  may  use  H  =  1;  0  =  16;  N  =  14;  0  =  12,  etc. 

How  the  Relative  Weights  of  the  Atoms  are  Determined. 

— If  we  could  isolate  atoms  and  weigh  them,  there  would 
be  no  serious  difficulty  in  determining  their  relative 
weights.  But  as  we  cannot  deal  with  atoms,  we  must 
deal  with  masses  of  atoms,  and  from  a  study  of  these 
masses  draw  conclusions  regarding  the  weights  of  the 
atoms. 

If  it  were  the  rule  that  two  elements  combine  with  each 
other  in  only  one  proportion,  it  might  be  safe  to  conclude 
that  they  combine  in  the  proportion  of  one  atom  of  one 
to  one  atom  of  the  other.  Then,  by  simply  determining 
the  relative  weights  of  the  elements  contained  in  a  mass 
of  the  compound,  we  should  be  in  a  position  to  draw  a 
conclusion  regarding  the  relative  weights  of  the  atoms. 
But  suppose  two  elements  combine  in  more  than  one  pro- 
portion. Suppose,  for  example,  that  nitrogen  and  oxygen 
combine,  as  they  do  very  nearly,  in  these  proportions:  14 


86  INTRODUCTION    TO  CHEMISTRY. 

of  nitrogen  to  8  of  oxygen,  7  of  nitrogen  to  8  of  oxygen, 

7  of  nitrogen  to  16  of  oxygen,  and  it  is  required  from  these 
figures  to  determine  the  relative  weights  of  the  atoms  of 
nitrogen  and  oxygen.     We  may  suppose  that  in  the  first 
compound  the  elements  are  combined  atom  to  atom,  then 
the  relative  weights  of  these  atoms  are  14  for  nitrogen  to 

8  for  oxygen.    If,  however,  we  had  already  concluded  from 
a  study  of  the  compounds  of  hydrogen  and  oxygen  that 
the   atom   of  oxygen   is  16  times  heavier  than  that  of 
hydrogen,   we   should  have  in  the   above   compound   of 
nitrogen  and  oxygen  28  parts  of  nitrogen  combined  with 
16  parts  of  oxygen,  and  the  atomic  weight  of  nitrogen 
would  appear  to  be  28.     But  we  may  equally  well  assume 
that  in  this  compound  2  atoms  of  nitrogen  are  combined 
with  1  atom  of  oxygen.     This  idea  would  be  represented 
by  the  formula  N20,  and,  if  we  accept  this  conception,  the 
atomic  weight  of  nitrogen  must  be  14.     This  example  will 
suffice  to  show  that  the   determination  of  the  relative 
weights  of  atoms  by  means  of  the  analysis  of  compounds 
is  a  difficult  matter,  and  that  attempts  to  make  the  deter- 
minations in  this  way  would  necessarily  lead  us  into  diffi- 
culties which  we  could  not  surmount  without  the  aid  of     ! 
some  new  conception  to  aid  us  to  determine  the  number 

of  atoms  contained  in  the  smallest  particles  of  compounds. 
The  difficulties  have  been   largely  overcome,  as  will  be 
shown  farther  on,  and  the  atomic  weights  accepted  at  the 
present  day  have  been  determined  by  the  aid  of  a  number     < 
of  methods. 

Formulas  of  Chemical  Compounds. — Molecules. — Chem- 
ical compounds  are  represented  by  placing  the  symbols  of 
the  constituent  elements  side  by  side.  Thus  HC1  means  a 
compound  of  hydrogen  and  chlorine  in  which  these  ele- 
ments are  present  in  the  proportion  of  1  part  by  weight  of 
hydrogen  to  35.18  parts  by  weight  of  chlorine,  or  in  terms 


FORMULAS  OF  CHEMICAL   COMPOUNDS.  87 

of  the  atomic  theory  it  means  a  compound  whose  smallest 
particle  is  made  up  of  an  atom  of  hydrogen  and  an  atom 
of  chlorine.  The  formula  H20  stands  for  a  compound 
whose  smallest  particle  is  made  up  of  two  atoms  of 
hydrogen  and  one  of  oxygen;  and  H?02  stands  for  a  com- 
pound whose  smallest  particle  consists  of  two  atoms  of 
hydrogen  and  two  atoms  of  oxygen.  The  small  figure 
placed  to  the  right  below  the  symbol  of  an  element  shows 
the  number  of  atoms  of  the  element  in  the  smallest  particle 
of  the  compound,  and,  of  course, — and  this  is  of  chief 
importance  at  this  stage, — it  shows  the  proportion  by 
weight  in  which  the  element  is  continued  in  the  compound. 
These  smallest  particles  of  compounds  are  called  molecules. 
The  relation  between  these  and  atoms,  and  the  methods  of 
determining  molecular  weights,  will  be  discussed  farther 
on.  The  formula  HC1  represents  then  a  molecule  of 
hydrochloric  acid  made  up  of  one  atom  of  hydrogen  and 
one  atom  of  chlorine;  H20  represents  a  molecule  of  water; 
HgO,  a  molecule  of  mercuric  oxide;  Mn02,  a  molecule  of 
manganese  dioxide;  KC103,  a  molecule  of  potassium 
chlorate;  ZnS04,  a  molecule  of  zinc  sulphate.  These 
formulas  are  of  great  convenience  in  representing  chemical 
reactions. 


CHAPTER  VI. 

STUDY  OF  THE  REACTIONS  EMPLOYED  IN  THE  PREP- 
ARATION OF  OXYGEN  AND  OF  HYDROGEN  AND 
IN  THE  STUDY  OF  WATER. 

Preparation  of  Oxygen. — The  reactions  employed  in  the 
preparation  of  oxygen  were:  (1)  The  decomposition  of 
mercuric  oxide  by  heat;  (2)  The  decomposition  of  potas- 
sium chlorate  by  heat;  (3)  The  decomposition  of  man- 
ganese dioxide  by  heat ;  and  (4)  The  action  of  heat  on  a 
mixture  of  potassium  chlorate  and  manganese  dioxide. 

Heating  Mercuric  Oxide.  —  When  mercuric  oxide  is 
heated  it  is  decomposed,  yielding  mercury  and  oxygen. 
This  was  shown  in  Exp.  3.  But  analysis  shows  that  mer- 
curic oxide  consists  of  mercury  and  oxygen  combined  in 
the  proportion  of  their  atomic  weights,  200  parts  of  mer- 
cury to  16  parts  of  oxygen;  and  it  has  been  shown  that 
when  decomposition  takes  place,  mercury  and  oxygen  are 
obtained  in  these  proportions.  These  facts  are  represented 
by  the  simple  equation 

HgO  =  Hg  +  0. 

This  equation  expresses  the  reaction  qualitatively  and 
quantitatively;  and  it  must  be  remembered  that  it  differs 
from  algebraic  equations  in  this  important  respect,  that  it 
expresses  something  that  has  been  established  by  experi- 
ment. Chemical  equations  cannot  be  solved  by  mental 
processes  alone,  as  algebraic  equations  can. 

88 


DECOMPOSITION  OF  POTASSIUM  CHLORATE  BY  HEAT.    89 

Quantitative  Study  of  the  Decomposition  of  Potassium 
Chlorate  by  Heat. — Potassium  chlorate  is  made  up  as 
represented  by  the  formula  KC103,  or  its  molecule  consists 
of  an  atom  of  potassium,  an  atom  of  chlorine,  and  three 
atoms  of  oxygen.  The  atomic  weights  of  these  elements 
are  respectively  K  =  39;  01  =  35.4;  and  0  =  16.  That 
is  to  say,  the  compound  consists  of  these  elements  in  the 
proportion  of  39  parts  of  potassium;  35.4  parts  of 
chlorine;  and  48(3  X  16)  parts  of  oxygen. 

It  is,  therefore,  an  easy  matter  to  calculate  how  much 
oxygen,  or  chlorine,  or*  potassium  any  given  weight  of 
potassium  chlorate  contains.  Let  it  be  required,  for 
example,  to  calculate  how  much  oxygen  is  contained  in 
4  grams  of  potassium  chlorate.  As  the  compound  is  made 
up  of  39  parts  of  potassium,  combined  with  35.4  parts  of 
chlorine  and  48  parts  of  oxygen,  in  39  -}-  35.4  -f-  48  = 
122.4  parts  of  potassium  chlorate  there  are  48  parts  of 
oxygen.  If  in  122.4  parts  there  are  48  parts,  how  much 
is  there  in  4  grams  ?  Plainly  the  answer  is  given  by  the 
solution  of  the  simple  proportion 

122.4  :48  ::4  :x, 

in  which  x  represents  the  actual  weight  of  oxygen  con- 
tained in  4  grams  of  potassium  chlorate.  Similarly  the 
proportion 

122.4  :39  ::4  :x 

will  give  the  weight  of  potassium,  and 
122.4  :35.4  ::4  :x 

will  give  the  weight  of  chlorine  contained  in  4  grams  of 
potassium  chlorate. 

When  potassium  chlorate  is  heated  until  no  more  oxygen 
is  given  off,  the  compound  potassium  chloride,  of  the 
formula  KC1,  is  left  behind.  By  weighing  the  potassium 


9°  INTRODUCTION   TO   CHEMISTRY. 

chlorate  taken  and  the  potassium  chloride  left,  and 
measuring  the  oxygen  given  off,  it  has  been  shown  that  the 
relative  weights  of  the  substances  are  represented  by  the 
equation 

KC103  KC1  + 

39  +  35.4  +  48  39  +  35.4 


That  is  to  say,  122.4  grams  of  potassium  chlorate  gives 
74.4  grams  of  potassium  chloride  and  48  grams  of  oxygen. 
The  figure  3  before  the  symbol  of  oxygen  means  three 
atoms  of  oxygen.  When  the  element  is  in  combination, 
the  figure  expressing  the  number  of  atoms  is  placed  to  the 
right  of  the  symbol,  below  the  line,  as  in  the  formula  of 
potassium  chlorate. 

EXPERIMENT  50.—  To  determine  how  much  oxygen  is  given  off 
when  a  known  weight  of  potassium  chlorate  is  decomposed  by 
heat,  proceed  as  follows  :  In  a  small  dry  hard-glass  tube  about  10 
cm.  (4  in.)  long  and  8  to  10  mm.  (about  £  in.)  internal  diameter, 
closed  at  one  end,  weigh  out  on  a  chemical  balance  about  0.2 


Fio.  26. 

gram  dry  potassium  chlorate,  first  weighing  the  tube  empty.  In- 
troduce just  above  the  potassium  chlorate  a  plug  of  asbestos, 
then  soften  the  tube  in  a  flame,  and  draw  it  out  so  that  it  has 
the  form  shown  in  Fig.  26,  the  plug  of  asbestos  being  at  the 
constricted  part  B  of  the  tube.  Now  weigh  the  tube  again. 

Let  a  —  weight  of  tube  empty  ; 

b  =  weight  of  tube  with  potassium  chlorate  ; 

c  =  weight  of  tube  with  potassium  chlorate  and  plug. 


DECOMPOSITION  OF  POTASSIUM  CHLORATE  BY  HEAT.    91 

Connect  at  A  by  means  of  a  short  piece  of  rubber  tubing  with 
a  measuring-tube  (see  Fig.  21)  so  that  the  ends  of  the  two  tubes 
are  almost  in  contact  with  each  other,  the  measuring-tube  having 
been  previously  filled  with  water  to  the  zero-point,  and  the  top 
closed  by  means  of  the  stop-cock.  Open  the  stop-cock,  and  now 
heat  the  potassium  chlorate,  gently  at  first,  and  gradually  higher 
until  no  more  gas  is  given  off.  After  the  gas  has  stood  for  half 
an  hour  to  cool  it  down  to  the  temperature  of  the  air,  adjust  the 
two  tubes  of  the  measuring-apparatus  so  that  the  level  of  the 
water  in  both  is  the  same  ;  read  off  the  volume  of  the  gas.  At 
the  same  time  read  the  barometer  and  thermometer ;  and  now 
make  the  corrections  for  pressure  and  temperature  as  directed 
pages  57-60.  The  weight  of  a  litre  or  1000  cc.  of  oxygen  at  0° 
and  760  mm.  pressure  is  1.429  grams.  Knowing  the  volume  of 
oxygen  obtained,  calculate  the  weight  of  this  volume.  Remove 
the  tube  containing  the  product  left  after  the  decomposition  of 
the  potassium  chlorate,  and  weigh  it. 

Let  d  =  weight  of  tube  after  decomposition  of  potassium  chlo- 
rate. Then 

5  _  a  =  weight  of  potassium  chlorate  used, 
c  —  d  =  loss  in  weight  =  oxygen. 

This  should,  of  course,  be  the  same  as  the  weight  of  oxygen 
found  by  measuring  that  given  off  and  calculating  the  weight 
from  the  volume. 

Further,  c  —  b  =  weight  of  plug  ; 

and  d  =  weight  of  tube  +  weight  of  plug    + 

weight  of  potassium  chloride  ; 
and    d  —  (a  +  c  —  6)  =  weight  of  potassium  chloride. 

Make  all  the  calculations,  and  see  how  nearly  the  results  ob- 
tained agree  with  the  equation 

KC103  =  KC1  +  3O. 

Should  the  results  not  be  satisfactory  the  first  time,  repeat  the 
work.  The  more  carefully  the  work  is  done  the  more  nearly  will 
the  results  agree  with  the  equation. 

In  Exp.  17  a  fact  was  observed  which  is  not  taken 
account  of  in  the  equation  KC103  =  KOI  -f-  30.  It  was 
seen  that  the  gas  was  given  off  in  two  stages :  first,  a  part 
came  off  at  a  comparatively  low  temperature,  and  then  a 


92  INTRODUCTION   TO   CHEMISTRY. 

larger  quantity  came  off  at  a  higher  temperature.  If  the 
gas  given  off  during  the  first  stage  had  been  measured,  it 
would  have  been  found  to  be  only  one  third  of  the  total 
obtained  by  complete  decomposition.  If,  further,  the  solid 
substance  left  behind  in  the  flask  had  been  properly  ex- 
amined, it  would  have  been  found  to  consist  of  two  sub- 
stances, one  of  which  was  potassium  chloride,  KC1,  and 
the  other  a  compound  that  contains  more  oxygen  than  the 
chlorate.  The  latter  is  potassium  perchlorate,  KC104. 
The  relative  quantities  of  the  two  substances  would  also 
have  been  found  to  correspond  to  the  weights  represented 
by  the  formulas  KC1  and  KC104,  i.e.,  there  would  have 
been  found  39  -j-  35.4  =  74.4  parts  of  potassium  chloride 
to  39  -f  35.4  +  4  X  16  =  138.4  parts  of  potassium  per- 
chlorate. The  following  equation  expresses  these  facts : 

2KC103  =  KC1  +  KC104  +20. 

The  figure  2  placed  before  the  formula  of  potassium 
chlorate  affects  the  whole  formula,  so  that  the  quantitative 
relations  are  represented  thus: 

2KC103         =      KOI     +        KC104         +     20. 
2(39-j-35.4-f48)     39  +  35.4     39  +  35.4+64      2x16 

2448  744  138J~  32 

In  the  second  stage  of  the  decomposition  all  the  rest  of 
the  oxygen  is  given  off,  or,  in  other  words.,  the  potassium 
perchlorate  is  now  decomposed,  thus : 

KC104  =  KC1  +  40. 

[PROBLEMS. — How  much  potassium  chlorate  must  be  taken  to 
get  10  litres  of  oxygen  ?  In  this  case  how  much  potassium  per- 
chlorate and  how  much  potassium  chloride  would  be  formed  ? 
How  much  potassium  chloride  would  5  grams  of  potassium  chlo- 
rate yield  ?  How  much  potassium  perchlorate  ?  What  volume  of 
oxygen  would  be  obtained  by  heating  20  grams  of  potassium 
chlorate  until  the  first  stage  of  the  decomposition  is  complete  ?] 


HEATING  MANGANESE  DIOXIDE,  93 

Heating  Manganese  Dioxide. — The  change  effected  in 
manganese  dioxide  by  heat  is  represented  by  the  equation 

•   .    3Mn02  =  Mn304  -f  20. 

The  atomic  weight  of  manganese  being  55,  the  quanti- 
tative relations  may  be  readily  calculated. 

[PROBLEMS. — How  much  oxygen  can  be  obtained  by  heating  12 
grams  of  majnganese  dioxide?  How  much  manganese  dioxide 
must  be  heated  in  order  to  get  3  grams  of  oxygen  ?  In  each  case 
how  much  of  the  compound  Mn3O4  would  be  obtained  ?] 

The  Action  of  Oxygen  on  Carbon,  Sulphur,  Phosphorus, 
and  Iron. — The  general  character  of  the  action  of  oxygen 
on  the  elements  named  has  been  discussed  in  connection 
.with  Experiments  21,  22,  23,  and  24,  and  evidence  was 
presented  to  show  that  the  action  consists  in  direct  union 
which  results  in  the  formation  of  new  compounds  called 
oxides.  But  the  quantitative  relations  were  not  referred 
to.  These  relations  must,  of  course,  be  determined  by 
experiment.  The  substance  burned,  the  oxygen  used 
up,  and  the  product  formed  must  in  each  case  be  weighed. 
This  has  been  done  repeatedly,  and  it  will  suffice  here  to 
give  the  results. 

When  sulphur  burns  in  oxygen,  for  every  32  parts  of 
sulphur  burned  32  parts  of  oxygen  are  used  up,  and  64 
parts  of  sulphur  dioxide,  S02 ,  are  formed : 

S  +     20      =         S02. 

32       2  X  16       32  +  2  X  16 

32  64 

In  the  case  of  carbon  it  has  been  shown  that  for  every 
12  parts  of  carbon  burned  32  parts  of  oxygen  disappear, 
and  there  are  formed  44  parts  of  the  compound  carbon 
dioxide,  C02.  The  equation  representing  the  action  is 

C  +     20      =         C02 

12       2  X  16       12  +  2  X  16 


94  INTRODUCTION   TO   CHEMISTRY. 

In  the  case  of  phosphorus,  for  every  62  parts  of  this 
element  which  disappear,  80  parts  of  oxygen  are  used  up, 
and  142  parts  of  the  compound  P20.  are  formed,  as  repre- 
sented in  the  equation 

2P     +     50     =  P205. 

2  X  31      5x16      2  X  31  -f  5  X  16 

The  compound  P20.  is  known  as  phosphorus  pentoxide. 
It  is  the  white  substance  found  in  the  vessel. 

When  iron  burns  in  oxygen  the  product  formed  is  mag- 
netic oxide  of  iron,  Fe^ : 

3Pe     -f     40     =  Fe304. 

3  X  56       4  X  16       3  X  56  -f4  x  16 

168  64  168  64 

Preparation  of  Hydrogen. — The  reactions  by  which 
hydrogen  can  be  most  readily  prepared  are:  (1)  The 
decomposition  of  water  by  an  electric  current;  (2)  The 
action  of  sodium  and  of  potassium  on  water;  (3)  The  action 
of  iron  on  water;  (4)  The  action  of  carbon  on  water;  (5) 
The  action  of  metals  on  acids. 

Decomposition  of  Water  by  an  Electric  Current. — This 
reaction  has  been  studied  somewhat  fully  in  connection 
with  the  subject  of  water.  The  facts  established  show 
that  it  is  represented  by  the  equation 

H20  =  2H  +  0. 

Action  of  Sodium  and  Potassium  on  Water. — Substitu- 
tion.— The  fact  that  when  sodium  is  thrown  on  water 
hydrogen  is  given  off  was  shown  in  Exp.  27.  Attention 
was  also  called  to  the  fact  that  there  is  something  in  the 
water  after  the  action  is  over.  Analysis  of  this  substance 
has  shown  that  it  has  the  composition  represented  by  the 
formula  NaOH.  It  is  called  caustic  soda  or  sodium 


ACTION  OF  IRON  ON   WATER.  95 

hydroxide.     The  reaction    between    sodium  and  water   is 
represented  by  the  equation 

Na  +  H20  ==  NaOH  +  II. 

According  to  this,  each  molecule  of  water  gives  up  one 
atom  of  hydrogen  and  an  atom  of  sodium  takes  its  place^ 
The  sodium  is  substituted  for  hydrogen  in  the  water. 
This  action  is  plainly  different  in  kind  from  any  that  has 
thus  far  been  studied.  These  are  either  simple  acts  of 
combination,  as  in  the  action  of  oxygen  on  sulphur;  or  of 
decomposition,  as  in  the  action  of  heat  on  mercuric  oxide 
and  on  potassium  chlorate.  The  action  of  sodium  on 
water,  however,  is  an  act  of  substitution,  which  involves 
both  combination  and  decomposition.  The  water  is 
decomposed  and  the  sodium  hydroxide  is  formed  by  com- 
bination. Potassium  acts  upon  water  in  the  same  way  as 
sodium,  and  the  reaction  is  represented  thus : 

K  +  H20  =  KOH  +  H. 

Potassium  acts  on  water  more  rapidly  than  sodium  does, 
so  that  the  amount  of  heat  evolved  in  a  given  time  is 
greater  than  in  the  case  of  sodium,  and  the  temperature  is 
therefore  raised  high  enough  to  set  fire  to  the  hydrogen. 
If  the  motion  of  the  sodium  is  interfered  with  by  placing 
on  the  water  a  piece  of  filter-paper  and  throwing  the  metal 
on  this,  the  temperature  becomes  high  enough  to  set  fire 
to  the  gas,  as  in  the  case  of  potassium.  This  restriction 
of  the  motion  of  the  sodium  simply  prevents  it  from  being 
cooled  off,  as  it  is  when  it  moves  over  the  surface  of  the 
water. 

Action  of  Iron  on  Water. — At  ordinary  temperatures 
iron  does  not  readily  act  on  water,  but  when  steam  is  passed 
over  heated  iron,  as  in  Exp.  28,  action  takes  place  accord- 
ing to  this  equation : 

3Fe  +  4H20  =  Fe30,  +  8H. 


96  INTRODUCTION   TO  CHEMISTRY. 

(In  what  other  experiment  has  the  compound  Fe304  been 
obtained  ?  What  is  its  name  ?) 

[PROBLEMS. — The  atomic  weight  of  iron  is  56  ;  how  much  water 
can  be  decomposed  by  20  kilograms  (or  40  pounds)  of  iron  ? 
and  how  much  would  the  hydrogen  obtained  weigh  ?  One  litre 
of  hydrogen  at  0°  C.  and  under  the  standard  pressure  of  760  mm. 
weighs  0.08995  gram  ;  what  will  be  the  volume  of  hydrogen  ob- 
tained by  using  up  20  kilograms  of  iron  in  the  decomposition  of 
water  ?] 

Decomposition  of  Water  by  Carbon. — This  decomposi- 
tion gives  the  mixture  known  as  < '  water-gas. "  The  action 
is  represented  by  the  equation 

C  +  H20  =  CO  +  2H. 

The  gas  CO  is  carbon  monoxide,  which  will  be  studied 
later. 

[PROBLEM. — The  reaction  represented  by  the  last  equation 
yields  equal  volumes  of  carbon  monoxide  and  of  hydrogen.  How 
much  water  would  5  kilograms  (or  10  pounds)  of  carbon  decom- 
pose, and  what  volume  of  gas  would  be  obtained  ?] 

Action  of  Metals  on  Acids. — The  action  of  zinc  on 
hydrochloric  acid  and  on  sulphuric  acid  was  studied  in 
Exp.  29,  and  it  was  stated  that  in  each  case  the  zinc  takes 
the  place  of  the  hydrogen  in  the  acid.  The  two  reactions 
are  thus  represented : 

(1)  2HC1     +     Zn     =     ZnCl2      +      2H. 

Hydrochloric  Acid.  Zinc  Chloride. 

(2)  H2S04     +     Zn     =     ZnS04    +      2H. 

Sulphuric  Acid.  Zinc  Sulphate. 

In  Exp.  30  the  zinc  sulphate  formed  was  obtained  in  the 
form  of  crystals.  It  will  be  seen  that  the  action  of  zinc 
on  hydrochloric  acid  and  on  sulphuric  acid  is  of  the  same 
kind  as  the  action  of  sodium  and  of  potassium  on  water. 
It  is  substitution.  The  zinc  takes  the  place  of  the  hy- 


ACTION  OF  ACIDS   ON  METALS. 


97 


drogen.  Another  point  of  interest  to  be  noted  is  that 
while  an  atom  of  sodium  takes  the  place  of  one  atom  of 
hydrogen,  an  atom  of  zinc  takes  the  place  of  two  atoms  of 
hydrogen.  It  will  be  seen  later  that  there  are  elements 
whose  atoms  have  the  power  of  taking  the  place  of  three 
atoms  of  hydrogen,  and  others  with  still  higher  substituting 
values. 

Quantitative  Study  of  the  Action  of  Acids  on  Metals,— 
One  example,  that  of  sulphuric  acid,  will  suffice. 

EXPERIMENT  51. — The  amount  of  hydrogen  evolved  when  a 
known  weight  of  zinc  is  dissolved  in  sulphuric  acid  can  be  de- 
termined by  means  of  the  apparatus  represented  in  Fig.  27.  The 


FIG.  27. 

bent  tube  leading  from  the  flask  A  is  drawn  out  at  B,  and  a  plug 
of  glass-wool  introduced  below  the  constriction.  The  other  parts 
of  the  apparatus  need  no  description.  The  flask  should  have  a 
capacity  of  about  40  to  50  cc. ;  and  the  measuring-tube  C  should 
have  a  capacity  of  about  100  cc.,  and  be  graduated  in  TV  cc.  Fill 
D  with  distilled  water  that  has  been  boiled  ;  put  a  piece  of  zinc 
weighing  from  0.15  to  0.20  gram  in  the  flask  ;  open  the  pinch- 
cock  E,  by  which  means  the  whole  apparatus  is  filled  with  water. 
Examine  the  apparatus  to  see  whether  gas-bubbles  are  lodged 


98  INTRODUCTION   TO  CHEMISTRY. 

under  the  stopper  For  in  the  glass-wool.  If  so,  they  can  usually 
be  dislodged  without  difficulty.  If  they  persist,  boil  the  water  for 
a  few  moments.  Now  place  the  measuring-tube  C  in  position  and 
let  the  greater  part  of  the  water  remaining  in  D  flow  through  the 
apparatus.  Into  this  tube  D  then  pour  sulphuric  acid  (1  of  acid 
to  4  of  water)  until  it  is  nearly  full.  Open  the  pinch-cock  E,  and 
thus  displace  the  water  which  fills  the  apparatus.  The  action  of 
acid  upon  the  metal  is  facilitated  by  heat  or  by  adding  with  the 
zinc  a  few  small  pieces  of  platinum.  When  the  action  is  over, 
sweep  the  contents  of  the  flask  through  the  delivery-tube  by  again 
opening  the  pinch-cock  E.  Finally,  the  measuring-tube  is  trans- 
ferred to  a  cylinder  of  water  (see  Fig.  22),  and  the  volume  of  the 
gas  read  and  corrected  in  the  usual  manner.  How  much  does  the 
hydrogen  obtained  in  the  experiment  weigh  ?  How  much  ought 
to  have  been  obtained?  How  many  cubic  centimetres  ought  to 
have  been  obtained  ? 

Action  of  Hydrogen  on  Copper  Oxide. — In  Exp.  46  it 
was  shown  that  when  hydrogen  is  passed  over  heated  copper 
oxide,  water  is  formed  and  copper  is  left  in  the  tube.  The 
action  is  represented  by  the  equation 

CuO  +  2H  =  H20  +  Oil. 

Here,  it  will  be  observed,  two  atoms  of  hydrogen  take  the 
place  of  one  atom  of  copper  in  the  oxide.  (Compare  the 
action  of  zinc  on  sulphuric  acid  with  that  of  hydrogen  on 
copper  oxide.) 

[PROBLEM. — The  atomic  weight  of  copper  is  63.6  ;  how  much 
water  would  be  formed  by  reducing  5  grams  of  copper  oxide  ? 
How  much  hydrogen  would  be  necessary?] 

Preparation  of  Hydrogen  Dioxide. — Double  Decomposi- 
tion.— Hydrogen  dioxide  consists  of  hydrogen  and  oxygen 
combined  in  the  proportion  of  1  part  by  weight  of  hydrogen 
to  16  parts  by  weight  of  oxygen.  By  methods  which  will 
be  discussed  later  it  will  be  shown  that  the  molecule  of  this 
compound  consists  of  two  atoms  of  hydrogen  combined 


KINDS  OF  CHEMICAL  REACTION.  99 

with  two  atoms  of  oxygen,  its  formula  being  H202.  Its 
formation  from  barium  dioxide  by  the  action  of  sulphuric 
acid  is  represented  thus : 

Ba02      -f     H2S04      =       BaS04     +     H202. 

Barium  Dioxide.     Sulphuric  Acid.        Barium  Sulphate. 

In  some  respects  this  reaction  differs  from  all  others  thus 
far  studied.  Here,  two  compounds  acting  upon  each  other 
give  two  new  compounds.  There  is  an  exchange  of  con- 
stituents. This  kind  of  action  is  called  double  decomposi- 
tion, or  metathesis.  It  is  by  far  the  most  common  kind  of 
chemical  action  with  which  we  have  to  deal. 

Kinds  of  Chemical  Reaction. — There  are  then  four  kinds 
of  chemical  reactions,  and  all  these  have  been  illustrated 
by  examples.  They  are:  (1)  Direct  Combination;  (2) 
Direct  Decomposition;  (3)  Substitution;  and  (4)  Double 
Decomposition)  or  Metathesis. 

Conditions  under  which  Chemical  Reactions  Take  Place. 

— Chemical  reactions  take  place  under  the  greatest  variety 
of  conditions.  Some  take  place  by  simply  bringing  the 
substances  together  at  ordinary  temperature,  as,  for  ex- 
ample, when  sodium  and  potassium  act  on  water.  Others 
take  place  on  heating  the  substances  together,  as,  for 
example,  when  iron  decomposes  water,  and  hydrogen 
decomposes  copper  oxide.  In  most  of  the  reactions  thus 
far  studied,  and  indeed  in  most  of  those  which  will  be 
studied,  heat  is  employed,  as  it  generally  aids  chemical 
action.  Some  reactions  take  place  in  solution.  That  this 
is  a  great  aid  to  chemical  action  has  already  been  pointed 
out  (see  page  70).  Some  substances  are  so  unstable  that 
they  are  decomposed  with  violence  by  the  touch  of  a 
feather,  as,  for  example,  a  compound  of  iodine  and  nitro- 
gen. Others  are  so  stable  that  they  resist  the  action  of 


ioo  INTRODUCTION   TO   CHEMISTRY. 

the  highest  temperatures.  The  electric  current  has  a  very 
marked  effect  upon  many  chemical  compounds,  especially 
if  they  are  in  solution  or  in  molten  condition.  This  has 
been  illustrated  by  the  action  of  the  current  on  water,  the 
result  being,  as  will  be  remembered,  the  setting  free  of  the 
two  gases  oxygen  and  hydrogen.  Again,  reactions  differ 
very  much  in  respect  to  their  violence,  from  the  most 
terrific  explosions  to  the  quiet  action  of  the  air  in  our 
lungs,  and  of  carbon  dioxide  in  the  leaves  of  plants. 


CHAPTER  YIL 

CHLORINE  AND   ITS  COMPOUNDS  WITH  HYDROGEN 
AND   OXYGEN. 

Occurrence. — Chlorine,  though  widely  distributed  in 
nature,  does  not  occur  in  very  large  quantity  as  compared 
with  oxygen  and  hydrogen.  It  is  found  chiefly  in  com- 
bination with  the  element  sodium  as  common  salt,  or 
sodium  chloride,  which  has  the  composition  represented 
by  the  formula  NaCl.  It  is  also  found  in  combination 
with  other  elements,  as  potassium,  magnesium,  etc.  In 
comparatively  small  quantity  it  occurs  in  combination  with 
silver,  forming  one  of  the  most  valuable  silver  ores. 

Preparation. — The  simplest  method  of  preparing  chlo- 
rine and  the  one  that  is  almost  exclusively  used  on  the 
large  scale  consists  in  passing^  a  strong  electric  current 
through  a  water  solution  of  potassium  chlori3e7~~TMs — 
causes  cnlorme'and  potassiurnTb~appear  at  the  poles  of  the 
battery.  The  chlorine  escapes  as  such,  while  the  potassium 
acts  upon  the  water,  forming  hydrogen  and  potassium 
hydroxide  or  caustic  potash.  Chlorine  is  also  obtained  by 
the  action  of  an  electric  current  on  a  solution  of  zinc 
chloride;  on  molten  sodium  chloride  to  which  other  sub- 
stances have  been  added  to  lower  the  melting-point;  and 
on  some  other  compounds  of  chlorine. 

In  the  laboratory  chlorine  is  made  by  oxidizing  hydro- 

101 


102  INTRODUCTION    TO   CHEMISTRY. 

chloric  acid.     Under  proper  conditions  the  action  repre- 
sented in  the  following  equation  takes  place : 

anci  +  o  =  iifl  +  aci. 

Deacon's  Process. — As  there  is  an  unlimited  supply  of 
oxygen  in  the  air,  it  would  be  advantageous  to  effect  the 
decomposition  of  hydrochloric  acid  by  means  of  the  ele- 
ment in  the  free  state.  On  the  large  scale-  this  is  now 
accomplished.  Deacon's  process  for  manufacturing  chlo- 
rine consists  in  passing  air  and  hydrochloric  acid  together 
through  a  heated  tube  containing  clay  balls  saturated  with 
copper  sulphate.  Exactly  why  the  oxidation  takes  place 
under  these  circumstances  is  not  known.  The  essential 
feature  of  the  reaction  is  nevertheless  the  oxidation  of  the 
hydrochloric  acid,  as  represented  in  the  above  equation. 

Laboratory  Method. — For  the  preparation  of  chlorine  in 
the  laboratory  it  is  most  convenient  to  bring  hydrochloric 
acid  in  contact  with  manganese  dioxide,  MnOz,  a  sub- 
stance which  has  been  employed  for  the  purpose  of  prepar- 
ing oxygen.  The  action  is  explained  thus :  In  the  first 
place,  when  hydrochloric  acid  acts  upon  many  compounds 
containing  oxygen,  the  hydrogen  and  oxygen  combine,  and 
the  element  which  was  in  combination  with  oxygen  com- 
bines with  chlorine.  Thus,  when  the  compound  MnO  is 
treated  with  hydrochloric  acid,  this  reaction  takes  place : 

MnO  +  2HC1  =  MnCl,  -f-  H20. 

So,  also,  when  manganese  dioxide  is  treated  with  hydro- 
chloric acid,  chlorine  is  probably  first  substituted  for  the 
oxygen,  as  represented  in  the  equation 

Mn02  +  4HC1  = 


LABORATORY  METHOD.  103 

But  the  compound  MnCl4  gives  up  half  of  its  chlorine 
when  heated  : 

MnCl4  =  MnCl2  -f  2C1. 

So    that    the    action  of  hydrochloric  acid  on  manganese 
dioxide  is  represented  as  follows  : 

Mn02  +  4HC1  =  MnCl2  +  2H20  +  2CL 

[PROBLEM.  —  How  much  manganese  dioxide  would  be  required 
to  liberate  50  grams  of  chlorine  ?  The  combining  weight  of  man- 
ganese is  55.] 

Instead  of  first  making  the  hydrochloric  acid  from  salt 
and  then  treating  the  hydrochloric  acid  with  manganese 
dioxide,  it  is  simpler  to  mix  together  the  manganese 
dioxide  and  common  salt  and  pour  upon  the  mixture  the 
necessary  quantity  of  sulphuric  acid.  The  reaction  takes 
place  according  to  the  following  equation  : 


The  products  formed  are  sodium  sulphate,  Na2S04, 
manganese  sulphate,  MnS04,  water,  H20,  and  chlorine. 

When  sulphuric  acid  acts  upon  sodium  chloride  alone 
the  products  are  sodium  sulphate,  Na2S04,  and  hydro- 
chloric acid,  HC1: 

SNaCl  +  H2S04  =  Na2S04  +  2HC1. 

EXPERIMENT  52.—  Pour  2  or  3  cc.  concentrated  sulphuric  acid 
on  a  gram  or  two  of  common  salt  in  a  test-tube.  Heat  gently. 
Describe  all  that  you  observe.  Hydroc-hloric  acid  is  formed. 
Give  some  account  of  it. 

EXPERIMENT  53.  —  This  experiment  should  be  carried  on  under 
a  hood.  Arrange  an  apparatus  as  shown  in  Fig.  28.  The  flask 
need  not,  of  course,  be  of  the  shape  shown  in  the  figure,  but  may 


104 


INTRODUCTION    TO   CHEMISTRY. 


Fiff.  28. 


be  of  any  kind  available.  It  should  have  a  capacity  of  about  1 
litre.  The  delivery-tube  should  extend  to  the  bottom  of  the  collect- 
ing vessel,  which  should  be  a  clean,  dry  cylinder  or  bottle  of  color- 
less glass.  The  mouth  of  this  vessel  should 
be  covered  with  a  piece  of  paper  to  prevent 
currents  of  air  from  carrying  away  the 
chlorine.  By  the  color  the  experimenter  can 
judge  of  the  quantity  of  chlorine  present 
in  the  vessel.  A  satisfactory  method  of 
making  chlorine  is  this  :  Mix  5  parts  by 
weight  of  coarsely  granulated  common  salt 
and  5  of  coarsely  granulated  manganese 
dioxide.  Make  a  mixture  of  12  parts  by 
weight  of  concentrated  sulphuric  acid  and 
6  of  water.*  Let  this  mixture  cool  down 
to  the  ordinary  temperature,  and  then  pour 
it  on  the  mixture  of  manganese  dioxide 
and  common  salt.  Use  50  grams  manga- 
nese dioxide  and  the  other  substances  in  the  proper  proportion. 
Heat  very  gently  and  collect  six  or  eight  dry  cylinders  or  bottles 
full  of  chlorine. 

(1)  Sprinkle  into  one  of  the  vessels  containing  chlorine  a  little 
finely  powdered  antimony.     The  two  elements  combine  at  once 
with   evolution  of  light.     The  product  is   antimony  trichloride, 
SbCU. 

[In  what  respects  does  this  experiment  resemble  the  one  in 
which  iron  was  burned  in  oxygen  ?  In  what  respects  do  the  two 
differ  ?] 

(2)  Into  a  second  vessel  introduce  a  few  pieces  of  heated  thin 
copper  foil,  or  a  sheet  of  Dutch  foil.     Combination  takes  place 
with  evolution  of  light  and  heat. 

(3)  Into  a  third  vessel  introduce  a  piece  of  paper  with  some 
writing  on  it,  some  flowers,  and  pieces  of  colored  calico.    Most 
of  the  colors  will  be  destroyed  if  the  substances  are  moist. 

(4)  Into  a  fourth  vessel  introduce  a   dry  piece  of  the  same 
colored  calico  as  that  used  in  the  previous  experiment.      What 
difference  do  you  observe  between  the  dry  piece  and  the  moist 
piece  ? 


*  See  precautions  noted  on  page  43. 


PROPERTIES  OF  CHLORINE.  105 

Properties  of  Chlorine.— Chlorine  is  a  greenish-yellow 
gas.  It  has  a  disagreeable  smell,  and  acts  upon  the 
passages  of  the  throat  and  nose,  causing  irritation  and 
inflammation.  The  effect  is  much  like  that  of  a  "  cold  in 
the  head."  Inhaled  in  concentrated  condition,  i.e.,  not 
diluted  with  a  great  deal  of  air,  it  would  cause  death.  It 
is  much  heavier  than  air,  its  specific  gravity  being  2.49. 
A  litre  of  chlorine  gas,  under  standard  conditions,  weighs 
3. 22  grms.  It  is  soluble  in  water,  acts  upon  mercury,  and 
therefore  cannot  be  collected  by  displacement  of  either  of 
these  liquids.  The  most  convenient  way  to  collect  it  is 
by  displacement  of  air  as  in  the  experiment.  It  is  easily 
condensed  to  the  liquid  form,  and  it  can  now  be  had  in  the 
market  in  this  f orm* 

Action  of  Chlorine. — From  these  experiments  it  is  seen 
that  chlorine  combines  readily  with  other  substances,  and 
also  that  it  destroys  colors,  or  bleaches.  It  is  indeed  one 
of  the  most  active  elements.  It  not  only  acts  directly 
upon  many  of  the  elements  at  ordinary  temperatures,  and 
decomposes  many  compounds,  but  it  also  acts  upon  most 
organic  substances,  or  such  as  are  formed  as  the  products 
of  animal  or  vegetable  life.  Its  action  upon  the  tissues  of 
the  respiratory  organs  has  already  been  noticed. 

EXPERIMENT  54. — Perform  this  experiment  under  a  hood.  Cut 
a  piece  of  filter-paper  or  tissue-paper  about  an  inch  wide  and  six 
to  eight  inches  long.  Pour  on  this  some  ordinary  oil  of  turpen- 
tine previously  warmed  slightly.  Introduce  this  into  a  vessel  of 
chlorine.  What  takes  place  ? 

Oil  of  turpentine  consists  of  carbon  and  hydrogen. 
The  main  action  of  the  chlorine  in  this  'case  consists  in 
extracting  the  hydrogen  and  leaving  the  carbon.  The 
experiment  is  interesting  chiefly  in  so  far  as  it  illustrates 
the  general  tendency  of  chlorine  to  act  upon  vegetable 
substances. 


Io6  INTRODUCTION   TO   CHEMISTRY. 

Bleaching  by  Chlorine. — It  has  been  iioticed  that  when 
moisture  is  present  chlorine  bleaches,  while  when  it  is  not 
present  bleaching  does  not  take  place.  It  has  been  shown 
that  chlorine  acts  directly  upon  some  dyestuffs,  converting 
them  into  colorless  substances.  In  other  cases  the  destruc- 
tion of  the  color  is  due  to  oxygen,  which  is  set  free  from 
water  by  the  action  of  chlorine.  In  the  direct  sunlight 
chlorine  decomposes  water  according  to  this 
equation : 

2C1  +  H20  =  2HC1  +  0. 

In  bleaching,  this  decomposition  of  water 
takes  place  in  direct  contact  with  the  colored 
materials,  and  the  oxygen,  the  instant  it  is 
set  free,  is  more  active  than  free  oxygen. 
It  is  tins  oxygen  which  is  being  set  free  that 
acts  upon  the  colored  substances  and  converts 
them  into  colorless  substances. 

EXPERIMENT  55.— Seal  the  end  of  a  glass  tube 
about  a  metre  (or  about  a  yard)  long  and  about 
12  mm.  (|  inch)  internal  diameter.    Fill  this  with 
FIG.  29.  a  strong  solution  of  chlorine  in  water.     Invert  it, 

as  shown  in  Fig.  29,  in  a  shallow  vessel  containing  some  of  the 
same  solution  of  chlorine  in  water.  Place  the  tube  in  direct  sun- 
light. What  takes  place  ?  What  change  in  color  of  the  solution, 
in  the  odor,  taste  ?  Examine  the  gas.  What  does  it  appear  to 
be? 

Chlorine  Hydrate. — When  chlorine  gas  is  passed  into 
water  cooled  down  almost  to  the  freezing-point,  crystals 
appear  in  the  vessel.  These  consist  of  chlorine  and  water 
and  are  known  as  chlorine  hydrate.  Its  composition  is 
represented  by  the  formula  Cl  -j-  5H20.  The  crystals  are 
very  unstable,  breaking  up  at  the  ordinary  temperature 
into  chlorine  gas  and  water. 

EXPERIMENT  56. — Light  a  jet  of  hydrogen  in  the  air  and  care- 


HYDROGEN  BURNS  IN  CHLORINE,  107 

fully  introduce  it  into  a  vessel  containing  chlorine.  Does  it  con- 
tinue to  burn  ?  Is  there  any  change  in  the  appearance  of  the 
flame  ?  Is  there  any  evidence  of  the  formation  of  a  gas  that 
differs  from  hydrogen  and  from  chlorine  ?  In  what  other  experi- 
ments lias  this  gas  been  met  with  ? 

Hydrogen  Burns  in  Chlorine, — The  ease  with  which 
chlorine  decomposes  water  and  vegetable  substances  con- 
taining hydrogen  shows  that  it  readily  combines  with 
hydrogen.  Just  as  hydrogen  burns  in  oxygen,  it  also  burns 
in  chlorine. 

The  burning  of  hydrogen  in  air  or  oxygen  is  simply  the 
act  of  combination  of  hydrogen  and  oxygen,  the  product 
being  water  in  the  state  of  vapor,  and  therefore  invisible. 
When  hydrogen  burns  in  chlorine  the  action  consists  in 
the  union  of  the  two  gases,  the  product  being  hydrochloric 
acid,  HC1,  which  forms  the  clouds  in  the  air.  In  both 
cases  the  action  is  accompanied  by  an  evolution  of  heat 
and  light. 

Chlorides. — J  ust  as  the  compounds  of  oxygen  with  other 
elements  are  called  oxides,  so  the  compounds  of  chlorine 
with  other  elements  are  called  chlorides. 

Nomenclature  of  Chlorides  and  of  Oxides. — Tho  chlorides 
are  named  in  the  same  way  as  the  oxides.  The  name  of 
the  element  with  which  the  chlorine  is  combined  is  pre- 
fixed. Thus  the  compound  of  zinc  and  chlorine,  ZnCl2 , 
is  called  zinc  chloride;  that  of  sodium  and  chlorine, 
sodium  chlorrde,  etc.  When  an  element  forms  more  than 
one  compound  with  oxygen,  suffixes  are  made  use  of  to 
distinguish  between  them.  Thus  in  the  case  of  copper 
there  are  two  oxides  which  have  the  formulas  Cu20  and 
CuO.  The  former,  which  contains  the  smaller  proportion 
of  oxygen,  is  called  cuprous  oxide,  while  the  latter,  which 
contains  the  larger  proportion  of  oxygen,  is  called  cupric 


io8  INTRODUCTION   TO   CHEMISTRY. 

oxide.  In  general,  of  two  oxides  of  the  same  element,  that 
which  contains  the  smaller  proportion  of  oxygen  is  desig- 
nated by  the  suffix  ous,  while  that  which  contains  the 
larger  proportion  is  designated  by  the  suffix  ic.  Ferrous 
oxide  has  the  composition  FeO;  ferric  oxide,  Fe203;  man- 
ganous  oxide  is  MnO;  manganic  oxide  is  Mn203.  In  case 
there  are  more  than  two  oxides  the  number  of  atoms  of 
oxygen  in  the  molecule  of  the  compound  is  frequently  in- 
dicated in  the  name.  Thus  manganese,  dioxide  is  MnO.,; 
sulphur  trioxide  is  SO 3;  phosphorus  pentoxide  is  P205,  etc. 
Chlorides  are  named  in  the  same  way.  Cuprous  chloride 
is  CuCl;  cupric  chloride  is  CuCl2;  ferrous  chloride  is  FeCl2; 
ferric  chloride  is  FeCl3;  phosphorus  trichloride  is  PC13; 
selenium  tetrachloride  is  SeCl4,  etc. 

Hydrochloric  Acid,  HC1. — The  only  compound  that 
chlorine  and  hydrogen  form  with  each  other  is  hydro- 
chloric acid.  It  has  already  been  shown  that  hydrogen 
burns  in  chlorine  and  that  hydrochloric  acid  is  formed. 
The  two  gases  may  be  mixed  and  allowed  to  stand  together 
indefinitely  in  the  dark  and  no  perceptible  action  will  take 
place.  If,  however,  the  mixture  is  put  in  diffused  sun- 
light, gradual  combination  takes  place;  and  if  the  direct 
light  of  the  sun  is  allowed  to  shine  for  an  instant  on  the 
mixture,  explosion  occurs,  and  this  is  the  sign  of  the  com- 
bination of  the  two  gases.  The  same  sudden  combination 
is  effected  by  applying  a  flame  or  spark  to  the  mixture,  or 
by  illuminating  it  instantaneously  with  an  electric  light  or 
the  light  from  a  piece  of  burning  magnesium. 

[What  difference  is  there  between  the  combination  of 
hydrogen  and  oxygen  and  of  hydrogen  and  chlorine  ?] 

Relation   of  Light   to   Chemical  Action. — The   way  in 

which  the  sunlight  and  other  bright  lights  act  upon  the 
mixture  of  hydrogen  and  chlorine  to  cause  them  to  com- 


PREPARATION  OF  HYDROCHLORIC  ACID.  109 

bine  is  not  understood;  but  the  fact  that  sunlight  does  have 
a  marked  influence  upon  some  kinds  of  chemical  action  is 
well  known.  One  other  illustration  of  this  influence  has 
already  been  presented,  that  of  the  decomposition  of  water 
by  chlorine.  This  action  does  not  take  place  in  the  dark. 
The  sunlight  is  essential.  The  art  of  photography  is 
based  upon  the  influence  of  light  in  causing  chemical 
changes.  The  light  from  the  object  photographed  is 
allowed  to  act  in  the  camera  on  a  plate,  upon  the  surface 
of  which  is  a  substance  that  is  changed  chemically  by  light. 
It  should  be  especially  noted  that  the  cause  of  the  chemical 
changes  in  these  cases  is  not  the  heat,  but  the  light.  If 
the  substances  are  heated  to  the  same  temperature  in  the 
dark,  the  changes  do  not  take  place. 

Preparation  of  Hydrochloric  Acid.  —  To  prepare  hydro- 
chloric acid,  common  salt  or  sodium  chloride,  NaCl,  is 
treated  with  sulphuric  acid  (see  Experiment  52,  page  103). 
The  hydrogen  of  the  sulphuric  acid  and  the  sodium  of  the 
salt  exchange  places,  as  represented  in  the  equation 

HS0   =  NaS0        2HC1. 


The  products  are  sodium  sulphate  and  hydrochloric  acid. 
The  hydrochloric  acid  is  given  off  as  a  gas,  and  the  sodium 
sulphate  remains  behind  in  the  flask. 

Properties.  —  Hydrochloric  acid  is  a  colorless  transparent 
gas.  It  has  a  sharp,  penetrating  taste  and  smell.  If  in- 
haled into  the  lungs  it  produces  suffocation.  It  dissolves 
in  water  very  readily.  At  ordinary  temperatures  one 
volume  of  water  will  dissolve  450  times  its  own  volume  of 
the  gas.  The  solution  is  the  liquid  known  in  the  labora- 
tory as  hydrochloric  acid. 

[PROBLEM.  —  A  litre  of  hydrochloric  acid  gas  weighs  1.6283  grams 
at  0°.  At  0°  one  volume.  of  water  will  absorb  500  times  its  own 


1 10  INTRODUCTION   TO   CHEMISTRY. 

volume  of  the  gas.  How  much  will  a  litre  of  water  increase  in 
weight  at  0°  by  taking  up  all  the  hydrochloric  acid  it  can  ?] 

So  readily  does  hydrochloric  acid  combine  with  water 
that  it  condenses  moisture  from  the  air;  hence,  although 
the  gas  itself  is  quite  colorless  and  transparent,  when  it 
comes  in  contact  with  the  air  dense  white  clouds  are 
formed,  which  are  not  formed  if  it  is  kept  from  contact 
with  the  air. — Hydrochloric  acid  does  not  burn  and  does 
not  support  combustion.  This  is  equivalent  to  saying  that 
it  does  not  combine  with  oxygen  under  ordinary  circum- 
stances, and  that  substances  which  combine  with  the 
oxygen  of  the  air  do  not  combine  with  hydrochloric  acid. 

[What  evidence  have  you  had  that,  under  some  circum- 
stances, oxygen  does  act  on  hydrochloric  acid  ?  What  are 
the  circumstances  ?  What  are  the  products  ?] 

Commercial  hydrochloric  acid  is  a  yellowish  liquid,  the 
color  being  due  to  the  presence  of  impurities.  It  is 
obtained  by  the  action  of  steam  on  magnesium  chloride : 

MgCl2  +  H20  =  MgO  +  2HC1. 

It  is  also  obtained  as  a  by-product  in  the  preparation  of 
sodium  sulphate  by  the  action  of  sulphuric  acid  on  sodium 
chloride. 

Pure  hydrochloric  acid  is  a  solution  of  the  pure  gas  in 
pure  water.  It  is  colorless,  and  when  concentrated  it 
gives  off  fumes  when  exposed  to  the  air.  The  solution 
when  heated  gives  off  a  large  part  of  the  gas  contained  in 
it,  and*  by  boiling  it  can  all  be  evaporated. 

EXPERIMENT  57.  Arrange  an  apparatus  as  shown  in  Fig.  30. 
The  flask  may  be  any  ordinary  one  of  about  1  litre  capacity. 
The  tubes  leading  into  the  Woulff  s  bottles  must  not  dip  in  the 
water  in  the  bottles.  If  they  end  a  few  millimetres  above  the 
surface  of  the  water  all  the  gas  will  be  absorbed. 


HYDROCHLORIC  ACID. 


in 


Weigh  out  5  parts  common  salt,  5  parts  concentrated  sulphuric 
add,  and  1  part  water.  Mix  the  acid  and  water,  taking  the 
usual  precautions  ;  let  the  mixture  cool  down  to  the  ordinary 
temperature  ;  and  then  pour  it  on  the  salt  in  the  flask.  For  the 
purposes  of  the  experiment  take  about  50  grams  of  salt.  Now 
heat  the  flask  gently,  and  the  gas  will  be  regularly  evolved. 
What  does  the  fact  of  the  sinking  of  the  solution  through  the 
water  indicate  ? — After  the  gas  has  passed  for  ten  to  fifteen  min- 
utes, disconnect  at  A,  and  let  some  escape  into  the  air.  Explain 
.what  you  see.  Blow  your  breath  towards  the  end  of  the  tube. 


FIG.  30. 

Does  this  produce  any  effect  ?  Explain  this.  Apply  a  lighted 
match  to  the  end  of  the  tube.  Does  the  gas  burn  ? — Collect  some 
of  the  gas  in  a  dry  cylinder  by  displacement  of  air,  as  in  the 
case  of  chlorine.  The  specific  gravity  of  the  gas  being  1.27,  the 
vessel  must  of  course  be  placed  with  the  mouth  upward.  That 
the  gas  is  colorless  and  transparent  is  shown  by  the  appearance 
of  the  generating-flask,  which  is  filled  with  the  gas.  Insert  a 
burning  stick  or  candle  in  the  cylinder  filled  with  the  gas.  What 
takes  place  ?  Does  the  gas  support  combustion  ?  Reconnect  the 
generating-flask  with  the  two  bottles  containing  water,  and  let  the 
process  continue  until  no  more  gas  comes  over.  The  reaction 
represented  in  the  equation 

SNaCl  +  H3S04  =  Na2S04  +  2HC1 

is  now  complete.  After  the  flask  has  cooled  down,  pour  water  on 
the  contents  ;  and  when  the  substance  is  dissolved  filter  it  and 


H2  INTRODUCTION   TO   CHEMISTRY. 

evaporate  to  such  a  concentration  that,  on  cooling,  some  of  the 
sodium  sulphate  is  deposited.  Pour  off  the  liquid  and  dry  the 
solid  substance  by  placing  it  upon  folds  of  filter-paper.  Compare 
the  substance  with  the  common  salt  which  you  put  in  the  flask 
before  the  experiment.  What  proofs  have  you  that  the  two  sub- 
stances are  not  the  same  ?— Heat  a  small  piece  of  each  in  a  dry  tube 
closed  at  one  end.  What  differences  do  you  notice  ? — Treat  a  small 
piece  of  each  in  a  test-tube  with  sulphuric  acid.  What  difference 
do  you  notice  ? — If  in  the  experiment  you  should  recover  all  the 
sodium  sulphate  formed,  how  much  would  you  have  ?  Put  about 
50  cc.  of  the  liquid  from  the  first  Woulff's  bottle  in  a  porcelain 
evaporating-dish.  Heat  over  a  small  flame  just  to  boiling.  Is 
hydrochloric  acid  given  off  ?— Can  all  the  liquid  be  driven  off  by 
boiling  ?— Try  the  action  of  the  solution  on  some  iron  filings.  What 
is  given  off  ?— Add  some  to  a  little  granulated  zinc  in  a  test-tube. 
What  is  given  off  ?  Add  a  little  to  some  manganese  dioxide  in  a 
test-tube.  What  is  given  off  ?— Add  ten  or  twelve  drops  of  the 
acid  to  2  to  3  cc.  water  in  a  test-tube.  Taste  the  dilute  solution. 
How  would  you  describe  the  taste  ?  Add  a  drop  or  two  of  a 
solution  of  blue  litmus,  or  put  into  it  a  piece  of  paper  colored  blue 
with  litmus.  The  color  is  changed  to  red.  Litmus  is  a  vegetable 
color  prepared  for  use  as  a  dye.  Other  dyes  are  changed  by 
hydrochloric  acid. — Make  a  solution  of  methyl  orange.  Add  a 
few  drops  of  the  solution  thus  obtained  to  dilute  hydrochloric 
acid.  Is  there  any  change  in  color? — In  each  case  add  a  few 
drops  of  a  solution  of  caustic  soda.  What  change  takes 
place  ? — In  what  experiment  has  caustic  .soda  been  obtained  ? 
What  relation  does  it  bear  to  water  ? — To  the  dilute  solution  of 
hydrochloric  acid  add  drop  by  drop  a  dilute  solution  of  caustic 
soda.  What  change  takes  place  in  the  taste  ? 

Analysis  of  Hydrochloric  Acid. — The  determination  of 
the  composition  of  hydrochloric  acid  is  not  as  easily  made 
as  that  of  water.  That  it  consists  of  hydrogen  and  chlorine 
is  shown  by  the  fact  that  it  is  formed  by  direct  combina- 
tion of  these  elements.  To  determine  the  relative  weights 
and  volumes  of  the  gases  that  enter  into  combination,  we 
may  proceed  thus:  Enclose  a  suitable  quantity  of  the  gas 
in  a  tube.  Introduce  a  small  piece  of  the  metal  potassium. 


ANALYSIS   OF  HYDROCHLORIC  ACID.  113 

Decomposition  will  take  place  as  represented  in  the  equa- 
tion 

K  +  HC1  =  KC1  +  H. 

The  gas  left  over  is  hydrogen.  On  measuring  its  volume 
it  will  be  found  to  be  just  half  that  of  the  hydrochloric 
acid  decomposed.  The  weight  of  the  hydrogen  obtained 
will  be  found  to  bear  to  the  weight  of  the  hydrochloric 
acid  the  proportion  1 :  36. 18.  In  other  words,  in  36. 18  parts 
of  hydrochloric  acid  there  are  35.18  parts  of  chlorine  and 
1  part  of  hydrogen.  In  1  volume  of  the  gas  there  is  ^ 
volume  of  hydrogen.  By  mixing  equal  volumes  of 
hydrogen  and  chlorine  and  causing  them  to  combine  it 
has  been  found  that  1  volume  of  hydrogen  combines  with 
1  volume  of  chlorine  to  form  2  volumes  of  hydrochloric 
.acid.  The  specific  gravity  or  the  relative  weights  of  equal 
volumes  of  hydrogen  and  chlorine  are:  hydrogen,  0.0696; 
chlorine,  2.49.  These  figures  bear  to  each  other  very 
nearly  the  same  relation  as  the  atomic  weights  of  the 
elements,  viz.,  1  :  35.18.  [What  fact  of  the  same  kind  was 
noticed  on  comparing  the  specific  gravities  of  hydrogen 
and  oxygen  ?]  Regarding  the  chemical  conduct  of  hydro- 
chloric acid,  the  experiments  already  performed  have 
shown : 

1.  That  when  in  solution  in  water  hydrogen  is  evolved 
when  this  solution  is  brought  in  contact  with  certain  sub- 
stances like  iron,   zinc,   etc.,   which  belong  to   the  class 
called  metals;  and  that  it  takes  up  the  metals  in  place  of 
the  hydrogen.     Thus  zinc  and  hydrochloric  acid  give  zinc 
chloride  and  hydrogen: 

Zn  +  2HC1  =  ZnCl2  +  2H. 

2.  That   in   contact   with   substances   which    give   off 
oxygen,  or  with  oxygen  itself  under  certain  circumstances, 
it  gives  up  its  chlorine,  while  the  hydrogen  combines  with 
oxygen  to  form  water. 


H4  INTRODUCTION    TO   CHEMISTRY. 

It  will  be  seen  hereafter  that  when  it  acts  upon  the 
compounds  of  the  metals  with  oxygen  or  the  so-called 
metallic  oxides  like  magnesia  or  magnesium  oxide,  MgO ; 
lime  or  calcium  oxide,  CaO;  zinc  oxide,  ZnO,  etc., — com- 
pounds which  do  not  easily  give  up  oxygen, — the  hydrogen 
of  the  acid  combines  with  the  oxygen  of  the  oxide  to  form 
water,  while  the  metals  combine  with  the  chlorine : 

MgO  +  2HC1  =  MgCl2  -f  H20; 
CaO  +  2HC1  =  CaCl2  +  H90; 
ZnO  +  2HC1  =  ZnCl2  +  H2"0. 

It  will  be  noticed  that  when  hydrochloric  acid  acts  upon 
zinc  oxide,  zinc  chloride  is  formed.  But  this  is  the 
product  obtained  when  hydrochloric  acid  acts  upon  the 
metal  zinc.  The  metals  calcium  and  magnesium  act 
towards  hydrochloric  acid  the  same  as  zinc.  Plainly  the 
cause  of  these  reactions  is  the  tendency  on  the  part  of 
chlorine  to  unite  with  the  metallic  elements. 

Action  of  Liquid  Hydrochloric  Acid. — What  has  been 
said  above  in  regard  to  the  action  of  hydrochloric  acid  has 
reference  to  the  solution  of  the  compound  in  water. 
Liquefied  hydrochloric  acid  does  not  give  off  its  hydrogen 
when  brought  in  contact  with  metals.  The  action  of  the 
water  is  in  this  case  of  prime  importance.  This  subject 
will  be  discussed  farther  on. 

Compounds  of  Chlorine  with  Oxygen  and  with  Hydrogen 
and  Oxygen. — As  has  been  seen,  chlorine  combines  very 
readily  with  hydrogen,  and  hydrogen  with  oxygen,  and  the 
products  are  stable  compounds.  On  the  other  hand, 
chlorine  cannot  be  made  to  combine  directly  with  oxygen. 
By  indirect  processes  they  can  be  combined,  but  the  com- 
pounds undergo  decomposition  easily,  yielding  back  the 
chlorine  and  oxygen  contained  in  them.  Before  taking 


COMPOUNDS   OF  CHLORINE.  115 

up  these  compounds  it  will  be  well  to  study,  as  far  as  may 
l^e  necessary,  the  compounds  of  chlorine,  hydrogen,  and 
oxygen  which  are  more -easily  made,  and  from  which  the 
oxides  are  made. 

Compounds  of  Chlorine  with  Hydrogen  and  Oxygen.— 

One  of  the  principal  reactions  made  use  of  for  the  prepara- 
tion of  compounds  of  chlorine,  oxygen,  and  hydrogen  is 
that  which  takes  place  when  potassium  hydroxide  is  treated 
with  chlorine.  The  products  are  different  according  to 
the  conditions.  It  seems  not  improbable  that  the  first 
change  is  one  of  substitution  as  represented  in  the  equa- 
tion 

KOH  +  C12  =  KOC1  -f  HOL 

The  hydrochloric  acid  thus  formed  would  not  escape  but 
would  at  once  act  upon  some  of  the  potassium  hydroxide. 
Thus 

KOH  4-  HC1  =  KC1  4-  H20. 

Combining  the  two  equations  we  have 

2KOH  +  C12  =  KOC1  +  KC1  +  H20. 

The  compound  represented  by  the  formula  KOC1  is  potas- 
sium li  ipoclilorite,  while  that  represented  by  the  formula 
KC1  13  potassium  chloride. 

If  the  solution  of  potassium  hydroxide  is  dilute  and  not 
allowed  to  become  hot,  the  change  above  represented  is  the 
principal  one  that  takes  place.  When,  however,  a  solution 
of  potassium  hypochlorite  is  heated  the  change  represented 
in  the  following  equation  takes  place : 

3KC10  =  2KC1  4-  KC103. 

The  compound  represented  by  the  formula  KC10  3  is  potas- 
sium chlorate. 


Ii6  INTRODUCTION    TO   CHEMISTRY. 

When  chlorine  is  passed  into  a  warm  concentrated  solu- 
tion of  potassium  Jiydroxide  this  second  change  takes 
place.  The  result  in  this  case  is  represented  thus : 

6KOH  -f  6C1  =  5KC1  +  KC103  +  3H20. 

Potassium  chlorate,  KC103 ,  and  potassium  hypochlorite, 
KC10,  bear  the  same  relation  to  two  compounds,  HC103 
and  HC10,  that  potassium  chloride,  KC1,  bears  to  hydro- 
chloric acid,  HC1,  or  sodium  chloride,  NaCl,  to  hydro- 
chloric acid.  But  hydrochloric  acid  can  be  easily  obtained 
from  sodium  chloride  by  adding  sulphuric  acid,  and 
potassium  chloride  undergoes  the  same  change  when 
treated  with  sulphuric  acid.  Further,  it  will  be  shown 
later  that  nearly  all  compounds  containing  sodium  or 
potassium  give  up  these  elements  when  treated  with  sul- 
phuric acid,  and  take  tip  hydrogen  in  their  place. 

On  treating  potassium  chloride  with  sulphuric  acid  this 
reaction  takes  place : 

2KC1  -f  H2S04  =  K2S04  -f-  2HC1. 

Similarly,  on  treating  potassium  chlorate  with  sulphuric 
acid,  this  reaction  takes  place : 

2KC103  +  H2S04  =  K2S04  -f  2HC103. 

The  products  are  potassium  sulphate  and  chloric  acid, 
HC103.  The  chloric  acid,  however,  is  very  unstable,  and 
decomposes,  yielding  other  compounds  of  chlorine.  The 
acid  itself  can  be  made  by  taking  proper  precautions,  but 
the  chief  interest  connected  with  it  is  the  fact  that  it 
decomposes  very  easily.  Potassium  chlorate,  which  is  so 
closely  related  to  it,  is  an  important  compound.  As  has 
been  shown,  it  gives  up  its  oxygen  under  the  influence  of 
heat.  It  also  gives  up  oxygen  when  brought  in  contact 
with  substances  that  have  the  power  to  unite  with  this 
element.  It  is  a  powerful  oxidizing  agent. 


POTASSIUM  HYPOCHLORITE.  II 7 

Potassium  hypochlorite,  KC10,  formed  by  passing  chlo- 
rine into  a  dilute  solution  of  caustic  potash,  is  decomposed 
by  sulphuric  acid  thus: 

2KC10  +  H2S04  =  K2S04  +.  2HC10. 

The  products  are  potassium  sulphate  and  liypochlorous 
acid.  If  a  concentrated  solution  of  potassium  hypochlorite 
is  treated  with  sulphuric  acid,  the  hypochlorous  acid 
formed  at  once  undergoes  decomposition,  yielding  chlorine, 
water,  and  oxygen.  The  acid  itself  is  not  well  known. 
The  principal  compound  related  to  it  is  bleaching-powder, 
or  the  substance  generally  known  as  "chloride  of  lime," 
which  is  familiar  to  every  one  on  account  of  its  applica- 
tion as  a  disinfecting  agent.  This  is  made  by  passing 
chlorine  into  slaked  lime,*  which  from  a  chemical  point 
of  view  is  analogous  to  caustic  potash.  Just  as  when 
chlorine  acts  on  a  dilute  solution  of  caustic  potash  a  mix- 
ture of  potassium  chloride  and  potassium  hypochlorite  is 
formed,  so  when  chlorine  acts  on  slaked  lime  a  mixture 
of  calcium  chloride,  CaCl2,  and  calcium  hypochlorite, 
Ca(OCl)2,  is  formed.  This  mixture  is  bleaching-powder. 
By  treating  it  with*  an  acid  it  gives  up  chlorine,  and  hence 
it  affords  a  convenient  means  of  transporting  chlorine. 
Thousands  of  tons  of  this  powder  are  manufactured  annu- 
ally. The  chlorine  is  passed  into  the  lime.  It  is  held 
chemically  combined  until  it  is  wanted,  when  it  can  be 
liberated  by  adding  an  acid  or  by  exposure  to  the  air. 

EXPERIMENT  58.— Dissolve  40  grams  (or  about  1£  ounces) 
caustic  potash  in  100  cc.  water  in  a  beaker-glass,  and  pass  into  it 
chlorine,  generated  as  in  Experiment  54,  but  from  75  grams  of 
salt  and  the  other  reagents  in  proportion.  Arrange  an  inverted 
funnel  on  the  end  of  the  delivery-tube  so  that  the  edge  of  the 
funnel  dips  just  below  the  surface  of  the  potash  solution,  to  pre- 
vent the  choking  of  the  delivery-tube.  When  the  solution  no 
longer  shows  an  alkaline  reaction  stop  the  action  and  boil  the 
solution  for  a  few  minutes  to  expel  the  excess  of  chlorine.  When 


n8  INTRODUCTION    TO   CHEMISTRY. 

the  solution  is  allowed  to  cool  crystals  of  potassium  chlorate 
mixed  with  a  little  potassium  chloride  will  separate  out.  These 
can  be  removed  by  nitration,  and  purified  by  recrystallization 
from  a  small  amount  of  water.  This  solution  should  be  filtered 
before  it  becomes  cool  enough  to  deposit  the  crystals.  Filter  off 
the  crystals  and  dry  them.  Is  the  substance  potassium  chlorate  ? 
Does  it  give  off  oxygen  when  heated  ?  In  a  dry  test-tube  pour  a 
drop  or  two  of  concentrated  sulphuric  acid  on  a  small  crystal  of 
it.  Do  the  same  with  a  piece  of  potassium  chlorate.  Hold  the 
mouth  of  the  test-tube  away  from  the  face.  What  is  noticed  in 
each  case? — Filter  and  evaporate  the  solution  from  which  the 
crystals  of  potassium  chlorate  have  been  removed.  On  allowing 
it  to  cool  crystals  will  again  be  deposited.  Take  them  out  and 
recrystallize  them.  Does  this  substance  give  off  oxygen  when 
heated  ?  Does  it  give  off  a  gas  when  treated  with  sulphuric  acid  ? 
Is  this  gas  colored  ?  If  the  gas  is  hydrochloric  acid,  what  is  the 
solid  substance  from  which  it  is  formed  ?  And  what  is  left  in 
the  test-tube  ? 

EXPERIMENT  59. — Place  the  slaked  lime,  made  by  slaking  20  to 
30  grams  of  quick-lime  with  enough  hot  water  to  make   a  dry 


FIG.  31. 


powder,  in  a  250-cc.  flask  with  a  two-hole  stopper.     Introduce  a 
glass  tube  through  one  of  the  holes  and  pass  chlorine  in  slowly, 


DECOMPOSITION  OF  BLEACHING-POIVDER  BY  ACIDS.    119 

keeping  the  flask  thoroughly  agitated,  for  about  ten  minutes. 
Introduce  a  funnel  and  delivery-tube  as  shown  in  Fig.  31. 
Pour  a  mixture  of  equal  parts  of  sulphuric  acid  and  water  slowly 
tnrough  the  funnel-tube.  Collect  by  displacement  of  air  the  gas 
given  off.  What  evidence  have  you  that  the  gas  is  chlorine  ? 

Decomposition  of  Bleaching-powder  by  Acids. — In   the 

last  experiment  the  substance  first  formed  is  bleaching- 
powder,  or  "chloride  of  lime."  This  is  decomposed  by 
sulphuric  acid,  yielding  chlorine.  The  formation  of 
chlorine  is  secondary,  and  due  to  the  ease  with  which 
hypochlorous  acid  breaks  up  into  chlorine,  oxygen,  and 
water.  The  tendency  of  sulphuric  acid  to  extract  calcium, 
just  as  it  does  potassium,  and  to  put  hydrogen  in  its  place, 
is  at  the  root  of  the  matter.  Potassium  hypochlorite  and 
potassium  chloride,  when  treated  with  sulphuric  acid, 
yield  primarily  hypochlorous  acid  and  hydrochloric  acid : 

2KC10  +  H,SO<  =  K2S04  +  2HC10; 
2KC1  +  H2S04  =  K2S04  +  2HC1. 

Thus  far  the  only  change  that  has  taken  place  is  the 
exchange  of  hydrogen  for  potassium.  Now,  however,  the 
hypochlorous  acid  is  decomposed,  yielding  oxygen,  water, 
and  chlorine,  probably  thus : 

2HC10  =  201  +  H20  +  0. 

The  oxygen  thus  liberated  would,  however,  act  upon 
hydrochloric  acid,  if  present,  and  set  chlorine  free: 

2H01  +  0  =  H20  +  201; 

so  that,  if  a  mixture  of  potassium  hypochlorite  and  potas- 
sium chloride  is  treated  with  sulphuric  acid,  we  should 
expect  the  result  to  be  that  which  is  represented  in  this 
equation : 

KC10  +  KC1  +  H,S04  =  K2S04  +  H,0  +  201. 
This  in  reality  expresses  what  takes  place,  as  has  been 
proved   experimentally.      The   decomposition  of   bleach- 


120  INTRODUCTION   TO   CHEMISTRY. 

ing-powder  takes  place  in  the  same  way,  the  only  differ- 
ence being  that  in  one  case  we  have  to  deal  with  compounds 
of  the  metal  potassium,  while  in  the  other  we  have  to  deal 
with  analogous  compounds  of  the  metal  calcium. 

As  bleaching-powder  is  easily  obtainable  it  affords  a 
convenient  means  of  preparing  chlorine  in  the  laboratory. 

Other  Compounds  of  Chlorine,  Hydrogen,  and  Oxygen. — 

While  the  remaining  compounds  of  chlorine,  hydrogen, 
and  oxygen  cannot  be  considered  here  in  detail,  a  refer- 
ence to  the  series  as  a  whole  will  serve  to  call  to  mind 
some  important  matters  of  general  interest.  There  are 
four  of  these  compounds  which,  as  far  as  composition  is 
concerned,  bear  a  very  simple  relation  to  one  another. 
They  are  hypochlorous  acid,  HC10;  chlorous  acid,  HC102; 
chloric  acid,  HC103;  and.  perchloric  acid,  HC104.  Begin- 
ning with  hydrochloric  acid,  we  have  thus  a  series  of  com- 
pounds, the  successive  members  of  which  differ  by  one 
atom  of  oxygen : 

Hydrochloric  acid HC1 

Hypochlorous  acid HC10 

Chlorous  acid HC102 

Chloric  acid HC103 

Perchloric  acid HC104 

This  series  illustrates  very  clearly  the  law  of  multiple, 
proportions  (see-ante,  p.  77).  [What  is  the  law  of  multiple 
proportions  ?  How  does  this  series  illustrate  the  law  ?] 

Compounds  of  Chlorine  and  Oxygen. — There  are  two  of 
these  compounds,  viz.,  chlorine  monoxide,  C120,  and 
chlorine  dioxide,  C102.  They  are  unstable  substances 
which  easily  break  up  into  chlorine  and  oxygen.  They 
are  not  easily  prepared  in  pure  condition. 


CHAPTER  VIII. 
ACIDS.— BASES.— NEUTRALIZATION.— SALTS. 

Neutralization. — It  is  now  time  to  inquire  what  features 
acids  have  in  common  that  lead  chemists  to  give  them  that 
name.  It  is  not  possible  to  understand  the  nature  of  their 
common  properties  without  a  somewhat  premature  refer- 
ence to  a  class  of  substances  to  which  special  attention  will 
be  called  in  due  time.  These  are  the  alkalies,  which  are 
the  most  marked  representatives  of  the  class  of  substances 
known  as  bases.  These  two  classes,  the  acids  and  the 
bases,  have  the  power  to  destroy  the  characteristic  proper- 
ties of  each  other.  When  an  acid  is  brought  in  contact 
with  a  base  in  proper  proportions,  the  characteristic 
properties  of  both  the  acid  and  the  base  are  destroyed. 
They  are  said  to  neutralize  each  other.  This  act  of 
neutralization  is  an  extremely  important  one,  with  which 
we  constantly  have  to  deal  in  chemical  operations. 

Litmus  Test  for  Acids  and  Alkalies, — The  most  common 
acids  are  sulphuric,  hydrochloric,  and  nitric  acids. 
Among  the  more  common  bases  are  caustic  soda,  caustic 
potash,  and  lime.  A  convenient  way  to  recognize  whether 
a  substance  has  acid  or  basic  properties  is  by  means  of 
certain  color-changes.  The  dye  litmus  is  blue.  If  a  solu- 
tion that  is  colored  blue  with  litmus  is  treated  with  a  drop 
or  two  of  an  acid,  the  color  is  changed  to  red.  If  now  the 
red  solution  is  treated  with  a  few  drops  of  a  solution  of  a 
base,  the  blue  color  is  restored.  There  are  many  other 

121 


122 


INTRODUCTION   TO   CHEMISTRY. 


substances  which  have  markedly  different  colors  in  acid 
and  in  alkaline  solutions.  A  solution  of  methyl  orange, 
for  example,  changes  color  when  treated  with  an  acid,  and 
recovers  its  color  when  again  treated  with  an  alkali. 

Quantitative  Study  of  Neutralization. — The  first  thing 
to  be  learned  in  regard  to  neutralization  is  whether  a 
definite  quantity  of  base  is  required  to  neutralize  a  definite 
quantity  of  an  acid. 

EXPERIMENT  60. — Make  dilute  solutions  of  nitric,  hydrochloric, 
and  sulphuric  acids  (4  cc.  dilute  acid,  such  as  is  used  in  the 
laboratory,  to  200  cc.  water)  ;  and  of  caustic  soda  and  caustic 

potash  (about  1  gram  to  200  cc.  of 
water).  Measure  off  a  definite 
quantity,  say  20  cc.,  of  each  of 
the  acid  solutions.  Add  a  few 
drops  of  a  solution  of  blue  litmus. 
Gradually  add  to  each  of  the 
measured  quantities  of  acid  suffi- 
cient dilute  caustic  soda  to  cause 
the  red  color  just  to  change  to 
blue.  As  long  as  the  solution  is 
red  it  is  acid.  When  it  turns  blue 
it  is  alkaline.  At  the  turning- 
point  it  is  neutral.  The  operation 
is  best  carried  on  by  means  of 
a  burette,  which  is  a  graduated 
tube  with  an  opening  from  which 
small  quantities  can  be  poured. 
A  convenient  shape  is  that  repre- 
sented in  Fig.  32.  At  the  lower 
end  is  a  small  opening.  The  flow 
of  the  liquid  from  the  burette  is 
controlled  by  means  of  a  pinch- 
cock.  It  will  require  some  prac- 
tice to  enable  the  student  to  know 
exactly  when  the  red  color  dis- 
appears and  the  blue  appears,  but 
with  practice  the  point  can  be  recognized  with  great  accuracy 


FIG.  3-». 


RATIO  OF  ACID   TO  ALKALI  IN  NEUTRALIZATION.   123 

Should  too  much  alkali  be  allowed  to  get  into  the  acid,  add  a  small 
measured  quantity  of  the  acid  from  another  burette.  Having  in 
one  experiment  determined  how  much  of  the  solution  of  alkali 
is  required  to  cause  the  red  color  to  change  to  blue  in  operating 
with  a  given  quantity  of  the  acid  solution,  try  the  experiment 
again,  using  a  different  quantity  of  the  acid  solution.  Perform 
similar  experiments  with  the  other  acids.  Afterwards  carefully 
examine  the  numerical  results.  If  the  work  has  been  properly 
done  the  ratio  between  the  volume  of  the  solution  of  any  given 
acid  and  that  of  any  given  base  will  always  be  found  to  be  the 
same  when  neutralization  is  completed.  The  work  should  be  re- 
peated until  the  results  are  satisfactory. 

Ratio  of  Acid  to  Alkali  in  Neutralization. — If  the 
results  of  several  experiments  with  the  same  acid  and 
alkali  are  recorded  it  will  be  found  that  there  is  a  definite 
ratio  between  the  quantities  of  acid  and  alkali  solution 
required  to  neutralize  one  another.  If,  for  example, 
15  cc.  of  the  alkali  solution  are  required  to  neutralize 
20  cc.  of  the  acid  solution,  18  cc.  of  the  alkali  solution 
will  be  required  to  neutralize  24  cc.  of  the  acid  solution, 
30  cc.  to  neutralize  40  cc.,  etc.  In  other  words,  in  order 
to  neutralize  a  given  quantity  of  an  acid,  a  definite 
quantity  of  an  alkali  is  necessary.  Suppose  15  cc.  of  the 
caustic-soda  solution  or  12  cc.  of  the  caustic-potash  solu- 
tion should  be  required  to  neutralize  20  cc.  of  the  hydro- 
chloric-acid solution.  If  the  quantities  of  these  alkali 
solutions  necessary  to  neutralize  equal  quantities  of  the 
other  acids  are  compared,  it  will  be  found  that,  if  it 
requires  15  cc.  caustic-soda  solution  or  12  cc.  caustic- 
potash  solution  to  neutralize  20  cc.  hydrochloric-acid  solu- 
tion, then  the  quantities  of  caustic-soda  solution  and 
caustic-potash  solution  required  to  neutralize  any  definite 
quantity  of  a  solution  of  another  acid  will  be  to  each  other 
as  15  to  12. 

What  is  Formed  when  Acid  and  Base  are  Neutralized? 
-It  appears,  therefore,  from  these  experiments  that  the 


124  INTRODUCTION   TO   CHEMISTRY. 

act  of  neutralization  is  a  definite  one,  which  takes  place 
between  definite  quantities  of  acid  and  base.  The  next 
question  that  suggests  itself  is,  What  is  formed  when  the 
acid  and  base  are  neutralized  ?  Experiment  must  answer. 

EXPERIMENT  61.— Dissolve  10  grams  caustic  soda  in  100  cc. 
water.  Add  hydrochloric  acid  slowly,  examining  the  solution 
from  time  to  time  by  means  of  a  piece  of  paper  colored  blue  with 
litmus.  As  long  as  the  solution  is  alkaline  it  will  cause  no 
change  in  the  color  of  the  paper.  The  instant  it  passes  the  point 
of  neutralization  it  changes  the  color  of  the  paper  to  red  ;  when 
exactly  neutral  it  will  neither  change  the  blue  to  red,  nor,  if  the 
color  is  changed  to  red  by  means  of  another  acid,  will  it  change 
it  back  again.  When  this  point  is  reached,  evaporate  off  the 
water  on  the  water-bath  to  complete  dryness,  and  see  what  is 
left.  Taste  the  substance.  Has  it  an  acid  taste  ?  Does  it  sug- 
gest any  familiar  substance  ?  If  it  is  sodium  chloride,  how  ought 
it  to  conduct  itself  when  treated  with  sulphuric  acid  ?  Does  it 
conduct  itself  in  this  way  ?  Satisfactory  evidence  can  be  given 
that  the  substance  is  sodium  chloride.  It  is  not  an  acid  nor  an 
alkali.  It  is  neutral.  Its  formation  took  place  according  to  the 
equation 

HC1  +  NaOH  =  NaCl  +  HaO. 

Using  nitric  acid  and  caustic  soda,  the  product  formed  is 
sodium  nitrate.  Compare  it  with  sodium  nitrate  from  the  labo- 
ratory bottle.  Heat  a  small  specimen  of  each  in  a  tube  closed  at 
one  end.  What  do  you  observe  ?  Treat  a  small  specimen  of  each 
with  a  little  sulphuric  acid  in  test-tubes.  What  do  you  observe  ? 

The  Reactions. — The  explanation  of  the  changes  which 
occur  in  these  cases  will  be  given  later.  Here  the  point 
to  be  noted  is,  that  the  substance  formed  when  nitric  acid 
acts  on  caustic  soda  is  sodium  nitrate.  The  reaction  took 
place  thus : 

Hisr03  -f  NaOH  =  NaN03  -f  H20. 

Similarly  sulphuric  acid  and  caustic  soda  give  sodium 
sulphate  and  water,  thus : 

H2S04  +  SNaOII  =  Na,S04  -f  2Ha6. 


WHAT   THESE  EXPERIMENTS  SHOW.  125 

With  caustic  potash  similar  reactions  take  place.  Hy- 
drochloric acid  and  caustic  potash  yield  potassium  chloride 
and  water: 

HC1  -f  KOH  =  KC1  +  H20. 

Nitric  acid  and  caustic  potash  yield  potassium  nitrate 
and  water: 

HNO,  -f  KOH  =  KN03  -f  H20. 

Sulphuric  acid  and  caustic  potash  yield  potassium  sul- 
phate and  water : 

H2S04  +  2KOH  =  K2SO,  +  2H20. 

What  these  Experiments  Show. — They  show : 

(1)  That  an  acid  contains  hydrogen; 

(2)  That  a  base  contains  a  so-called  metallic  element; 

(3)  That  when  an  acid  acts  on  a  base  the  hydrogen  and 
metallic  element  exchange  places; 

(4)  That  the  substance  obtained  from  the  acid  by  sub- 
stituting a  metallic  element  for  the  hydrogen  is  neutral; 

(5)  That  the  substance  formed  from  the  base  by  sub- 
stituting hydrogen  for  the  metallic  element  is  water. 

These  statements  are  of  general  application,  except 
statement  (4),  to  which  there  are  some  exceptions.  It  is 
true  in  some  cases  that  after  replacing  the  hydrogen  the 
substance  has  an  alkaline  reaction,  and  in  other  cases  that 
the  product  has  an  acid  reaction. 

It  has  been  shown  that  hydrochloric  acid  and  sulphuric 
acid  act  upon  certain  metals,  as  iron  and  zinc,  and  that 
the  action  consists  in  giving  up  hydrogen  and  taking  up 
metal  in  its  place.  The  products  of  this  action  are  the 
same  in  character  as  those  formed  by  the  action  of  acids 
on  bases. 

Importance  of  Water  in  the  Experiments  on  Neutraliza- 
tion.— One  fact  of  great  importance  is  not  taken  into 


126  INTRODUCTION  'TO   CHEMISTRY. 

consideration  in  what  has  thus  far  been  said  concerning 
neutralization.  It  is  this:  The  substances  must  ~be  brought 
together  in  solution.  Dry  hydrochloric  acid  and  dry 
potassium  hydroxide,  for  example,  do  not  act  upon  each 
other,  and  the  same  is  true  of  other  perfectly  dry  acids 
and  bases.  The  water  is  essential  to  the  action.  This 
raises  the  question : 

What  is  Solution  ? — No  satisfactory  answer  can  yet  be 
given  to  this  question.  There  are  many  liquids  besides 
water  in  which  solids  can  be  dissolved,  but  for  the  present 
attention  may  be  confined  to  solutions  in  water.  Of  these 
two  kinds  can  be  distinguished  between : 

(1)  The  solutions  of  some  substances  have  the  power  to 
conduct  electricity; 

(2)  The  solutions  of   other    substances   have   not    this 
power. 

Substances  of  the  first  class  are  called  electrolytes.  To 
this  class  belong  acids,  bases,  and  salts. 

Substances  of  the  second  class  are  called  non-electrolytes. 
To  this  class  belong  sugar  and  many  other  compounds  less 
familiar. 

There  is  good  reason  for  believing  that,  when  an  elec- 
trolyte is  dissolved  in  water,  a  part  of  the  substance  is 
broken  down  or  dissociated  into  simpler  parts  called  ions. 
Thus,  hydrochloric  acid  is  believed  to  break  down  to  a 
greater  or  less  extent  into  the  ions  H  and  Cl;  nitric  acid 
into  the  ions  H  and  N03;  chloric  acid  into  the  ions  II 
and  C103 ,  etc.  So  also,  sodium  hydroxide  is  believed  to 
break  down  into  the  ions  Na  and  OH;  potassium  hy- 
droxide into  the  ions  K  and  OH.  Further,  sodium 
chloride  is  believed  to  break  down  into  the  ions  Na  and  Cl; 
potassium  nitrate  into  the  ions  K  and  N03,  etc. 

The  extent  of  this  breaking  down  or  dissociation  (called 
electrolytic  dissociation)  is  determined  largely  by  the  dilu- 
tion— the  greater  the  dilution,  the  greater  the  dissociation. 


ACIDS  AND  BASES.  127 

Ions  not  the  Same  as  Atoms. — The  ions  which  are 
believed  to  be  present  in  the  solutions  of  electrolytes  are 
not  to  be  confounded  with  the  atoms  or  with  definite  com- 
pounds. The  atoms  of  which  the  molecule  of  hydrochloric 
acid  is  made  up  are,  to  be  sure,  hydrogen  and  chlorine. 
The  ions  into  which  the  molecule  of  hydrochloric  acid 
breaks  down  or  dissociates  when  dissolved  in  water  are 
these  atoms  highly  charged  with  electricity.  When  the 
electricity  is  discharged  the  elements  appear  in  their 
ordinary  forms. 

Definition  of  Acids  and  Bases  in  Terms  of  the  Theory  of 
Electrolytic  Dissociation. — If  the  views  above  presented 
are  correct,  and'  the  evidence  upon  which  they  rest  is 
undoubtedly  strong,  then  acids  and  bases  should  be  defined 
as  follows : 

(1)  An  acid  is  a  substance  that   gives   hydrogen  ions 
when  dissolved  in  water;* 

(2)  A  base  is  a  substance  that  gives  ions  of  the  composi- 
tion represented  by  the  formula  OH,  called  hydroxyl,  when 
dissolved  in  water. 

The  common  properties  of  acids — the  sour  taste,  the 
evolution  of  hydrogen  when  brought  together  with  metals, 
their  action  on  dyes,  their  power  to  neutralize  bases — are 
believed  to  be  due  to  the  fact  that  they  all  give  hydrogen 
ions. 

So  also  the  common  properties  of  bases — their  alkaline 
taste,  their  action  on  dyes,  their  power  to  neutralize  acids 
— are  believed  to  be  due  to  the  fact  that  they  give  hydroxyl 
ions. 

Products  of  Neutralization. — In  the  light  of  the  above 
ideas  what  conception  are  we  to  form  of  the  act  of  neutral- 
ization ?  When,  for  example,  hydrochloric  acid  and 

*  Some  other  solvents  act  like  water,  but  not  in  so  marked  a  way. 


128  INTRODUCTION   TO   CHEMISTRY. 

sodium  chloride  are  brought  together  in  solution  what  are 
the  changes  ?  Hydrochloric  acid  gives  the  ions  H  and  Cl; 
sodium  hydroxide  gives  the  ions  Na  and  Oil.  So  that  we 
have  at  first  in  the  water  solution  a  condition  which  may 
be  represented  thus : 

H  +  Cl  +  Na  +  OH. 

But  water  has  not  the  power  to  dissociate  water;  and  if  the 
constituents  of  water,  the  ions  II  and  OH,  find  themselves 
together,  they  unite  to  form  water.  We  should  therefore 
have 

H  -f  01  +  Na  +  OH  =  Cl  -|-  Na  +  H20. 

The  characteristic  hydrogen  ion  of  the  acid  and  the 
characteristic  hydroxyl  ion  of  the  base  would  thus  be 
removed  and  a  condition  of  neutrality  would  result.  The 
ions  01  and  Na  would  remain  uncombined  unless  the  solu- 
tion were  concentrated.  By  evaporating  off  the  water 
they  would  come  more  and  more  into  combination  and 
with  the  disappearance  of  the  water  they  would  wholly 
disappear  as  such,  and  in  their  place  we  should  have  the 
compound  sodium  chloride,  which  is  neutral. 

Salts. — When  an  acid  and  a  base  are  brought  together, 
then,  water  is  the  first  product  of  the  action.  The  other 
product  is  called  a  salt.  Thus  sodium  chloride,  NaCl, 
potassium  nitrate,  KN03,  potassium  chloride,  KC1,  etc., 
are  called  salts.  Comparing  these  salts  with  the  acids 
from  which  they  are  derived,  it  will  be  seen  that  they  are 
formed  from  these  by  the  substitution  of  the  elements 
sodium  and  potassium  for  the  hydrogen  of  the  acids : 

HOI  UNO, 

NaCl  NaN03 

KC1  KN03. 

Sodium  and  potassium  are  examples  of  a  class  of  ele- 
ments that  are  called  metallic  elements.  Speaking  broadly, 


METALLIC  ELEMENTS.  129 

a  salt  is  a  substance  formed  by  substituting  a  metallic 
element  for  the  hydrogen  of  an  acid. 

Metallic  Elements. — It  may  fairly  be  asked,  What  is 
a  metallic  element  ?  Unfortunately  for  our  present 
purpose,  it  is  by  no  means  easy  to  give  a  satisfactory 
answer  to  this  question.  Examples  of  metals  can  easily 
be  given,  such  as  iron,  zinc,  silver,  calcium,  magnesium, 
etc. ;  but  when  the  attempt  is  made  to  state  what  the  dis- 
tinguishing features  of  these  substances  are,  difficulties  are 
met  with.  In  general,  it  may  be  said  that  to  the  chemist 
any  element  is  metallic  which  with  hydrogen  and  oxygen 
forms  a  product  that  has  the  power  to  neutralize  acids ; 
that  is  to  say,  that  has  basic  properties.  In  general,  any 
element  that  has  the  power  to  enter  into  an  acid  in  the 
place  of  the  hydrogen  is  called  a  metal,  or  is  said  to  have 
metallic  properties.  This  is  the  sense  in  which  the  word 
metal  is  used  in  this  book. 

Nomenclature  of  Acids. — The  names  of  those  acids  of 
chlorine  which  contain  oxygen  illustrate  some  of  the  prin- 
ciples of  nomenclature  in  use  in  chemistry.  That  acid  of 
the  series  which  is  best  known  is  called  chloric  acid.  The 
termination  ic  is  generally  used  in  naming  acids,  as  is  seen 
in  the  names  hydrochloric,  sulphuric,  nitric,  etc.  If  a 
second  acid  containing  the  same  elements  exists  and  the 
proportion  of  oxygen  contained  in  it  is  smaller  than  in  the 
acid  the  name  of  which  ends  in  ic,  the  second  acid  is  given 
a  name  ending  in  ous.  Thus  chlorous  acid  contains  a 
smaller  proportion  of  oxygen  than  clilorjc  acid,  and  the 
suffixes  ic  and  ous  signify  that  fact.  There  are  many  other 
examples  of  this  use  of  these  suffixes  in  the  names  of  acids 
as  well  as  in  the  names  of  compounds  of  other  classes. 

In  the  series  of  chlorine  acids,  however,  this  simple 
principle,  which  is  sufficient  for  most  cases,  does  not 


13°  INTRODUCTION   TO   CHEMISTRY. 

suffice.  In  order,  therefore,  to  form  characteristic  names 
for  the  other  members  of  the  series  recourse  is  had  to 
prefixes.  There  is  one  acid  which,  so  far  as  the  proportion 
of  oxygen  contained  in  it  is  concerned,  stands  below 
chlorous  acid.  It  is  called  hypochlorous  aoid,  the  prefix 
hypo  being  derived  from  the  Greek  vno,  under.  Further, 
there  is  an  acid  which  contains  a  larger  proportion  of 
oxygen  than  chloric  acid.  It  is  called  perchloric  acid,  the 
Latin  prefix  per  signifying  here  vtry  01  fully.  It  will  be 
seen  that  the  names  of  the  acids  vary  with  the  proportion 
of  oxygen  contained  in  them. 

Nomenclature  of  Bases. — As  pointed  out  above,  a  base 
is  a  compound  of  a  metal  with  hydrogen  and  oxygen  or 
with  hydroxyl.  Thus,  caustic  soda  has  the  formula 
NaOH,  caustic  potash  KOH,  lime  Ca02H2 ,  etc.  They  are 
commonly  known  as  hydroxides.  In  order  to  distinguish 
between  the  hydroxides  of  the  different  metals,  the  names 
of  the  metals  are  put  before  the  name  hydroxide.  Thus, 
caustic  soda,  !NaOII,  is  called  sodium  hydroxide;  caustic 
potash,  KOH,  is  called  potassium  hydroxide;  caustic  lime, 
Ca02H2,  is  called  calcium  hydroxide,  etc.  They  are 
regarded  as  water  in  which  a  part  of  the  hydrogen  has 
been  replaced  by  a  metal,  and  indeed  many  of  them  can 
be  made  by  simply  bringing  the  corresponding  metals  in 
contact  with  water.  Thus,  as  has  been  seen  (Exp.  27, 
page  39),  when  sodium  or  potassium  is  thrown  on  water 
hydrogen  is  evolved.  The  products  formed  are,  respec- 
tively, sodium  hydroxide  and  potassium  hydroxide.  These 
compounds  are  called  hydrates  by  some  chemists,  the  name 
implying  that  they  are  derivatives  of  water.  The  name 
hydroxide  means  simply  that  the  substances  contain 
hydrogen  and  oxygen. 

Nomenclature  of  Salts.— Theoretically  every  metal  can 
yield  a  salt  with  every  acid.  The  salts  derived  from  a 


NOMENCLATURE   OF  SALTS.  131 

given  acid  receive  a  general  name,  and  this  general  name 
is  qualified  in  each  case  by  the  name  of  the  metal  contained 
in  the  salt.  Thus  all  the  salts  derived  from  nitric  acid 
are  called  nitrates;  all  the  salts  derived  from  chloric  acid 
are  called  chlorates;  the  salts  of  sulphuric  acid  are  called 
sulphates.*  So  too,  further,  the  salts  of  chlorous  acid  are 
called  chlorites;  those  of  nitrous  acid,  nitrites;  those  of 
sulphurous  acid,  sulphites,  etc.,  etc.  It  will  be  noticed 
that  the  terminal  syllable  of  the  name  of  the  salt  differs 
according  to  the  name  of  the  acid.  If  the  name  of  the 
acid  ends  in  ic,  the  name  of  the  salt  derived  from  it  ends 
in  ate.  If  the  name  of  the  acid  ends  in  ous,  the  name  of 
the  salt  ends  in  ite.  To  distinguish  between  the  different 
salts  of  the  same  acid,  the  name  of  the  metal  contained  in 
it  is  prefixed.  Thus,  the  potassium  salt  of  nitric  acid  is 
called  potassium  nitrate,  the  sodium  salt  is  called  sodium 
nitrate;  the  calcium  salt  of  sulphuric  acid  is  called  calcium 
sulphate;  the  magnesium  salt  of  nitrous  acid  is  magnesium 
nitrite.  The  calcium  salt  of  hypochlorous  acid  is  calcium 
hypochlorite,  etc.,  etc.  [Give  the  name  and  formula  of 
the  potassium  salt  of  perchloric  acid. — Give  the  name  and 
formula  of  the  sodium  salt  of  hypochlorous  acid. — Give  the 
name  and  formula  of  the  sodium  salt  of  chlorous  acid.] 

If  the  salts  of  hydrochloric  acid  were  named  in  accord- 
ance with  the  principle  just  explained,  they  would  be  called 
hydrochlorates.  But  it  will  be  observed  that  these  salts  are 
identical  with  the  products  formed  by  direct  combination 
of  the  metals  with  chlorine.  Thus,  hydrochloric  acid  and 
zinc  act  as  represented  in  the  equation 

Zn  +  2HC1  =  ZnCl2  +  2H, 
while  zinc  and  chlorine  act  thus : 

Zn  +  2C1  =  ZnCl2. 

*  If  the  principle  were  strictly  applied  the  salts  of  sulphuric  acid 
would  be  called  sulphurates,  but  for  the  sake  of  convenience  the 
name  is  shortened. 


132  INTRODUCTION    TO   CHEMISTRY. 

In  each  case  the  same  product,  ZnCl2 ,  is  formed.  But 
these  compounds  of  metals  with  chlorine  are  called 
chlorides,  as  has  already  been  explained.  Hence  the  name 
hydro  chlorate  is  unnecessary. 

Acid  Properties  and  Oxygen. — The  observation  that 
oxygen  is  generally  present  in  acids  .led  at  one  time  to  the 
belief  that  it  is  an  essential  constituent  of  these  substances. 
Hence  the  name  oxygen  was  given  to  it  (from  o£vs,  acid, 
and  yevvacsD,  I  form).  That  oxygen  is  not  essential  to  the 
existence  of  acid  properties  is  shown  in  the  case  of  hydro- 
chloric acid,  and  in  a  few  other  similar  cases.  Hydrogen 
is  the  element  that  is  essential  to  acids,  but  not  all 
hydrogen  compounds  are  acids,  as  shown,  for  example,  by 
the  bases  which  contain  hydrogen. 


CHAPTER  IX. 


NITROGEN.— AIR. 

Two  Gases  in  the  Air. — It  has  been  stated  that  when 
substances  burn  in  the  air  the  same  products  are  formed 
as  when  thej-brrfn  in  oxygen;  and,  further,  that  there  is 
something  besides  oxygen  pi  esent  in  the  air  which  renders 
the  burning  less  active  than  it  is  in  oxygen  alone.  When 
phosphorus  is  exposed  to  the  air  it  combines  slowly  with 
oxygen,  and  the  phosphorus  pemoxide  formed  easily  dis- 
solves in  water.  These  facts  may  be  utilized  for  the  pur- 
pose of  getting  possession  of  the  other 
gas  in  the  air,  as  this  does  not  combine 
with  phosphorus. 


\ 
of 


Quantitative  Study  of  the  Composition 
the  Air.  —  The  ratio   of  the  oxygen  of 


the  air  to   the  nitrogen 
mined  as  below. 


can  be  deter- 


EXPERIMENT 62.  —  Arrange  an  apparatus  as 
in  Fig.  33.  Use  a  tube  graduated  in  cubic 
centimetres.  Enclose  60  to  80  cc.  air  in  the 
tube  over  water.  Arrange  the  tube  so  that 
tUe-  level  of  the  water  inside  and  outside  is 
the  same.  Note  the  temperature  of  the  air 
and  the  height  of  the  barometer.  Reduce  the 
observed  volume  to  standard  conditions. 
Now  introduce  a  piece  of  phosphorus  fastened  FlG>  33- 

to  the  end  of  the  wire,  and  allow  it  to  stand  for  twenty-four 

133 


134  INTRODUCTION   TO   CHEMISTRY. 

hours.  Draw  out  the  phosphorus.  Again  arrange  the  tube  so 
that  the  level  of  the  water  inside  is  the  same  as  that  outside. 
Make  the  necessary  corrections  for  temperature,  pressure,  and 
pressure  of  water- vapor.  It  will  be  found  that  the  volume  has 
diminished  considerably,  but  that  about  four  fifths  of  the  gas 
originally  put  in  the  tube  is  still  there.  If  the  work  is  done 
carefully,  the  volume  of  the  gas  left  in  the  tube  will  be  to  the 
total  volume  used  as  79  to  100.  In  other  words.,  of  every  100  cc. 
air  used  21  cc.  are  absorbed  by  phosphorus,  and  79  cc.  are  not. 
The  experiment  should  be  repeated  two  or  three  times  and  the 
results  compared.  The  gas  absorbed  is  oxygen,  identical  with 
the  oxygen  made  from  the  oxide  of  mercury,  manganese  dioxide, 
and  potassium  chlorate.  The  gas  left  over  has  no  chemical  prop- 
erties in  common  with  oxygen.  Carefully  take  the  tube  out  of  the 
vessel  of  water,  closing  its  mouth  with  the  thumb  or  some  suit- 
able object  to  prevent  the  contents  from  escaping.  Turn  it  with 
the  mouth  upward,  and  intror*  ice  into  it  a  burning  stick.  What 
takes  place  ?  This  residual  gas  will  not  support  combustion,  and 
cannot  therefore  be  oxygen. 

Nitrogen. — ^ne-sexperiment  just  performed  shows  us 
that  the  air  -Is  made  up  by  volume  of  21  per  cent  of  oxygen 
and  79  per  cent  of  a  gas  that  does  not  support  combus'- 
tioT>. '  This  second  constituent  of  the  air  is  nitrogen. 

Preparation. — Anything  that  has  the  power  to  absorb 
oxygen  may  be  used  in  the  preparation  of  nitrogen  from 
the  air.  To  avoid  contamination  of  the  nitrogen  with 
other  substances,  however,  it  is  necessary  to  use  something 
which  does  not  form  a  gaseous  product  when  burned. 
Apppr  is  crmvfmientf  and  is  not  infrequently 
It  is  only  necessary  to  pass  air  over  heated  copper, 
when  the  _inetal  combines  with  oxygen,  forming  the  solid 
copper  oxide,  CuO,  leaving  the  nitrogen  uncombined. 
The  most  convenient  way  to  prepare  nitrogen  is  to  burn  a 
piece  of  phosphorus  in  a  bell-jar  over  water. 

EXPERIMENT  63. — Place  a  good-sized  stoppered  bell-jar  over 
water  in  n  pneumatic  trough.  In  the  middle  of  a  flat  cork  about 


3 


THE    AIR.  135 

three  inches  in  diameter  fasten  a  small  porcelain  crucible,  and 
float  this  on  the  water  in  the  trough.  Put  into  it  a  piece  of  phos- 
phorus about  twice  the  size  of  a  pea,  and  set  fire  to  it.--  Quickly 
place  the  bell-jar  over  it.  At  first  some  air  will  be  driven  out  of 
the  jar.  [WhyJ]  The  burning  will  continue  for  a  short  time,  and 
then  gradually  grow  less  and  less  active,  finally  stopping.  On 
cooling,  it  will  be  found  that  the  volume  of  gas  is  less  than  four 
fifths  the  original  volume,  for  the  reason  that  some  of  the  air 
was  driven  out  of  the  vessel  at  the  beginning  of  the  experiment. 
Before  removing  the  stopper  of  the  bell-jar  see  that  the  level  of 
the  liquid  outside  is  the  same  as  that  inside.  Try  the  effect  of 
introducing  successively  several  burning  bodies  into  the  nitrogen, 
— as,  for  example,  a  candle,  a  piece  of  sulphur,  phosphorus,  etc 

The  Air. — The  nitrogen  and  oxygen  which  make  up  the 
air  are  not  chemically  combined  with  each  other,  but 
simply  mixed  together.  It  is  not  an  easy  matter  to  prove 
this  statement,  but  the  evidence  is  so  strong  that  no 
chemist  doubts  it. 

(1)  If  nitrogen  and  oxygen  are  mixed  together,  the  mix- 
ture conducts  itself  in  exactly  the  same  way  as  air.     The 
mixing  is  not  accompanied  by  any  phenomena  indicating 
chemical  action.     Generally,  the  chemical  union   of  two 
substances  is  accompanied  by  a  change  in  their  tempera- 
ture.    When  nitrogen  and  oxygen  are  mixed  there  is  no 
change  in  the  temperature  of  the  gases. 

(2)  The  composition  of  a  chemical  compound  is  con- 
stant.    The  law  of  definite  proportions  is  founded  upon  a 
very  large  number  of  observations,   and  in  all  cases  in 
which  there  is  independent  evidence  that  chemical  action 
takes  place,  it  is  found  that  the  same  substances  combine 
in  the  same  proportions  to  form  the  same  product.     Vari.i- 
tion  in  the  composition  of  a  chemical  compound  is  not 
known.      The    composition    of    the    air    varies    slightly, 
according  to  circumstances. 

(3)  Air  dissolves  somewhat  in  water.     If  air  which  has 
been  thus  dissolved  is  pumped  out  and  analyzed,  it  is  found 


136  INTRODUCTION    TO   CHEMISTRY. 

to  have  a  composition  different  from  that  of  ordinary  air. 
Instead  of  containing  1  volume  of  oxygen  to  4  volumes  of 
nitrogen,  it  contains  1  volume  of  oxygen  to  1.87  volumes 
of  nitrogen.  The  relative  quantity  of  the  oxygen  is  much 
larger  in  air  that  has  been  dissolved  in  water  than  it  is  in 
ordinary  air.  This  is  due  to  the  fact  that  oxygen  is  more 
soluble  in  water  than  nitrogen  is.  In  order,  however,  that 
one  gas  may  dissolve  more  than  the  other,  it  is  necessary 
that  they  should  not  be  in  chemical  combination.  If  they 
were  in  chemical  combination  the  compound  as  such  would 
probably  dissolve. 

Occurrence  of  Nitrogen. — Besides  being  found  uncom- 
bined  in  the  air,  nitrogen  is  found  in  combination  in  a 
large  number  of  substances  in  nature.  It  is  found  in  the 
nitrates,  or  salts  of  nitric  acid,  particularly  as  the  potassium 
salt,  KN03,  known  as  saltpetre,  and  the  sodium  salt, 
NaN03 ,  known  as  Chili  s^altn^tce.  It  is  also  found  in  the 
form  of  ammonia,  which  is  a  compound  of  nitrogen  .and 
hydrogen,  represented  by  the  formula  NH3.  Ammonia 
occurs  in  small  quantity  in  the  air,  and  is  formed  under  a 
variety  of  conditions,  to  which  reference  will  be  made 
when  the  substance  is  presented.  Nitrogen  occurs, 
further,  in  most  animal  substances  in  chemical  combina- 
tion. 

Properties  of  Nitrogen. — It  has  been  seen  that  nitrogen 
is  a  colorless,  tasteless,  inodorous  gas.  It  does  not  support 
combustion,  nor  does  it  burn.  (Suppose  nitrogen  were 
combustible,  what  would  be  the  composition  of  the  atmos- 
phere ?)  Nitrogen  not  only  does  not  combine  directly 
with  oxygen  readily,  but  it  does  not  combine  directly  with 
any  other  element  except  at  very  high  temperature.  Just 
as  it  does  not'  support  combustion,  so  also  it  does  not  sup- 
port respiration.  An  animal  would  die  in  it,  not  on 


OTHER   CONSTITUENTS   OF  THE  AIR.  137 

account  of  any  active  poisonous  properties  possessed  by 
it,  but  for  lack  of  oxygen.  In  the  air  it  serves  the  useful 
purpose  of  diluting  the  oxygen.  If  the  air  consisted  only 
of  oxygen,  all  processes  of  combustion  would  certainly  be 
much  more  active  than  they  now  are,  What  the  effect  on 
animals  of  the  continued  breathing  of  oxygen  would  be,  it 
is  impossible  to  say.  The  atomi(T~weight  of  nitrogen  is 
14;  Q4.  ^Its  specific  gravity  isr0.967.  A  litre  of  nitrogen 
weighs  1.2507  gram.  Under  a  pressure  of  35  atmospheres 
and  below  —  146°  nitrogen  is  liquefied.  It  boils  at  —  194° 
under  the  ordinary  atmospheric  pressure.  Oxygen  boils 
at  —  181°,  or  13°  higher.  Nitrogen  can  also  be  obtained 
,  in  crystallized  form. 

Other  Constituents  of  the  Air. — Besides  nitrogen  and 
oxygen  the  air  contains  other  substances,  some  of  which 
are  of  great  importance. 

EXPERIMENT  64. — On  a  watch-glass  expose  a  few  pieces  of  cal- 
cium chloride  to  the  air.  What  change  takes  place,  and  how  is 
this  explained  ?  See  Experiment  42.  (What  is  a  salt  called  which 
has  the  power  to  take  up  water  from  the  air  and  dissolve  in  the 
water  ?) 

EXPERIMENT  65. — Lime-water  is  made  by  putting  a  few  pieces 
of  quick-lime  in  a  bottle  and  pouring  water  upon  it.  The  mix- 
ture is  well  shaken  and  allowed  to  stand.  The  undissolved 
substance  settles  to  the  bottom,  and  with  care  a  clear  liquid  can 
be  poured  off  the  top.  This  is  lime-water,  which  is  a  solution  of 
calcium  hydroxide,  Ca(OH)3,  in  water.  Baryta-water  is  a  solu- 
tion of  a  similar  compound  of  the  metal  barium.  Expose  some 
clear  lime-water  or  baryta-water  and  note  the  changes. 

When  these  solutions  are  exposed  to  nitrogen  or  oxygen, 
or  to  an  artificially  prepared  mixture  of  the  two  gases,  no 
change  takes  place.  Further,  if  air  is  first  passed  through 
a  solution  of  caustic  soda  it  no  longer  has  the  power  to 
cause  the  formation  of  a  crust  on  lime-water  or  baryta- 
water. 


138 


INTRODUCTION    TO   CHEMISTRY. 


EXPERIMENT  66. — Arrange  an  apparatus  as  shown  in  Fig.  34. 
The  wash-cylinders  A  and  B  are  half  filled  with  ordinary  caustic- 
soda  solution.  The  bottle  C  is  filled  with  water.  The  tube  D 
reaches  to  the  bottom  of  the  bottle.  Being  filled  with  water  and 
provided  with  a  pinch-cock,  it  acts  as  a  siphon.  Open  the  pinch- 
cock  and  let  the  water  flow  slowly  out  of  the  bottle.  As  it  flows 


FIG.  34. 

out,  air  will  be  drawn  in  through  the  caustic-soda  solution  in  the 
wash-cylinders.  When  the  bottle  is  filled  with  air  pour  some 
water  in  again  so  that  it  is  about  a  quarter  full.  Draw  this 
water  off  as  before.  Now  remove  the  stopper  from  the  bottle, 
pour  in  20  to  30  cc.  lime-water  and  cork  the  bottle.  Is  there  any 
difference  between  the  action  of  this  air  and  ordinary  air  ?  What 
difference  ? 

What  Causes  the  Difference? — It  appears,  therefore, 
that  there  is  something  present  in  the  air  under  ordinary 
circumstances  that  has  the  power  to  form  a  crust  on  lime- 
water  or  baryta-water,  and  this  can  be  removed  by  passing 
the  air  through  caustic  soda.  Thorough  examination  has 
shown  that  this,  is  the  compound  called  carbon  dioxide  or 
carbonic  acid  gas.  It  is  the  substance  obtained  by  burning 
charcoal  in  oxygen. 


CONSTITUENTS   OF  THE  AIR. 


139 


EXPERIMENT  67. — Into  the  bottle  containing  the  air  from  which 
the  carbon  dioxide  has  been  removed,  insert  a  burning  stick  or 
taper  for  a  moment.  Notice  whether  a  crust  is  now  formed  on 
the  lime-water.  Wood  and  the  material  from  which  the  taper  is 
made  contain  carbon.  Explain  the  formation  of  the  crust  on  the 
lime-water  after  the  stick  of  wood  or  taper  has  burned  for  a 
short  time  in  the  vessel. 

EXPERIMENT  68. — Arrange  an  apparatus  as  shown  in  Fig.  35. 
The  bottle  A  contains  air  ;  B  contains  concentrated  sulphuric 
acid  ;  C  is  carefully  dried  and  contains  a  few  pieces  of  granulated 
calcium  chloride  and  air.  Pour  water  through  the  funnel-tube 
into  A:  the  air  will  be  forced  through  B  and  into  C.  But  in 
passing  through  B  the  moisture  contained  in  it  will  be  removed 
and  the  air  which  enters  C  will  be  dry.  After  A  has  once  been 
filled  with  water,  empty  it  and  fill  it  again,  letting  the  dried  air 
pass  into  C.  This  operation  may  be  repeated  as  many  times  as 


FIG.  35. 


may  seem  desirable.     The  calcium  chloride  in  C  will  not  grow 
moist. 

Constituents  of  the  Air. — The  preceding  experiments 
show  that  besides  oxygen  and  nitrogen  there  are  present 
in  the  air  water,  in  the  form  of  vapor,  and  carbon  dioxide, 


140  INTRODUCTION  TO  CHEMISTRY. 

which  is  a  colorless  gas.  Wherever  we  examine  the  air 
these  two  subtances  are  found  to  be  present.  Indeed,  it 
is  evident  that  they  must  be  present.  Evaporation  is 
taking  place  everywhere,  even  at  low  temperatures,,  and 
the  vapor  thus  formed  is  carried  to  all  parts  of  the  earth 
by  the  winds.  Whenever  any  of  our  ordinary  combustible 
substances  burn  in  the  air,  carbon  dioxide  is  formed;  and, 
further,  the  process  of  respiration  of  animals  also  gives  rise 
to  the  formation  of  carbon  dioxide,  which  is  given  off  from 
the  lungs. 

Quantity  of  Water-vapor  in  the  Air. — The  quantity  of 
water-vapor  present  in  the  air  varies  between  comparatively 
wide  limits.  At  any  given  temperature  the  air  cannot? 
hold  more  than  a  certain  quantity.  When  it  contains  this 
quantity  it  is  said  to  be  saturated.  If  cooled  below  this 
temperature  the  vapor  partly  condenses  to  form  water. 
When  a  vessel  containing  ice-water  is  placed  in  the  air,  that 
which  immediately  surrounds  the  vessel  is  cooled  below  the 
point  at  which  the  quantity  of  water-vapor  present  would 
saturate  the  air,  and  water  is  deposited  on  the  vessel.  On 
a  warm  cloudy  day  more  water  is  deposited  on  a  cold  object 
than  on  a  clear  cool  day.  The  water-vapor  present  in  the 
air  has  an  important  effect  on  man.  Inhabitants  of 
countries  with  moist  climates  have  characteristics  not 
generally  met  with  in  those  who  live  in  dry  climates.  The 
difference  between  the  effect  of  moist  and  that  of  dry  air 
on  an  individual  is  well  known. 

When  air  charged  with  water-vapor  comes  in  contact 
with  cooler  air,  the  vapor  condenses  and  falls  as  rain. 

The  quantity  of  water-vapor  in  a  given  volume  of  air  can 
be  determined  by  drawing  the  air  through  a  weighed  tube 
containing  calcium  chloride.     The  increase  in  weight  wilj^ 
give  the  quantity  of  water  in  the  air  drawn  through  the 
tube. 


ARGON—LIQUID  AIR.  141 

Quantity  of  Carbon  Dioxide  in  the  Air. — The  quantity 
of  carbon  dioxide  in  the  air  is  only  about  3  parts  in  10,000 
parts.  It  varies  slightly  according  to  the  locality  and  the 
season.  It  is  essential  to  the  growth  of  plants. 

Argon. — After  all  the  carbon  dioxide,  water- vapor,  and 
oxygen  have  been  removed  from  the  air,  nitrogen  remains 
as  by  far  the  most  important  constituent.  But  at  least 
four  other  gases  are  mixed  with  it  in  small  quantities. 
The  principal  one  of  these  is  argon.  This  is  obtained : 

1.  By  passing  nitrogen,  obtained  as  above,  over  heated 
magnesium  which  absorbs  it  and  leaves  the  argon:  or 

2.  By  adding  oxygen  to  air  contained  in  a  vessel  inverted 
over  a  solution  of  sodium  hydroxide  and  provided  with  wires 
so  arranged  that  electric  sparks  can  be  passed  between  their 
ends  inside  the  vessel;  and  passing  sparks  for  a  long  time 
through  the  mixture.     The  oxygen  and  nitrogen  combine 
and   the   product   dissolves   in    the    solution   of   sodium 
hydroxide.     After  all  the  nitrogen  has  thus  been  removed 
argon  remains  behind.    "  It  is  an  extremely  inactive  sub- 
stance.    No  compounds  of  it  have  yet  been  obtained.     It 
is  present  in  the  air  to  trie  extent  of  about  1  per  cent  of 
the  nitrogen.     Its  atomic  weight  is  39.9. 

Liquid  Air. — By  subjecting  air  to  high  pressure  and 
then  letting  it  escape  through  a  needle-valve  it  is  cooled  to 
a  very  low  temperature.  If  this  cold  air  is  allowed  to  play 
upon  the  vessel  containing  the  compressed  air  the  latter  is 
partly  liquefied.  Very  efficient  machines  have  been  con- 
structed by  which  air  can  be  liquefied  in  any  desired 
quantity.  The  problem  of  its  practical  applications  has 
not  yet  been  worked  out. 

Oxygen  Prepared  from  Liquid  Air. — When  liquid  air  is 
allowed  to  stand  under  the  ordinary  pressure  of  the  atmos- 


M2  INTRODUCTION   TO   CHEMISTRY. 

phere  the  nitrogen  boils  off  together  with  some  of  the 
oxygen,  and  after  a  time  nearly  pure  liquid  oxygen  is  left. 
This  furnishes  a  method  of  obtaining  oxygen  from  the  air. 

Other  Gases  in  the  Air. — Besides  the  gases  mentioned 
above  very  small  quantities  of  three  other  gases  have  also 
been  found  in  the  air.  These  are  called  krypton,  neon, 
and  xenon.  Little  more  is  known  about  them  than  that 
they  occur  in  the  air. 


CHAPTER  X. 

COMPOUNDS   OF   NITROGEN  WITH    HYDROGEN    AND 
OXYGEN. 

General  Conditions  which  Give  Rise  to  the  Formation 
of  the  Simpler  Compounds  of  Nitrogen. — It  has  been  shown 
that  nitrogen  is  an  inactive  element,  manifesting  little 
tendency  to  combine  with  other  elements.  It  is  never- 
theless an  easy  matter  to  get  compounds  of  nitrogen  with 
many  other  elements,  and  among  these  compounds,  some 
of  those  which  it  forms  with  hydrogen  and  oxygen  are  the 
most  important. 

Whenever  a  compound  containing  carbon,  hydrogen, 
and  nitrogen  is  heated  in  a  closed  -vessel,  so  that  the  air 
does  not  have  access  to  it  and  it  cannot  burn  up,  the 
nitrogen  passes  out  of  the  compound,  not  as  nitrogen,  but 
in  combination  with  hydrogen,  in  the  form  of  the  com- 
pound called  ammonia.  Nearly  all  animal  substances 
contain  carbon,  hydrogen,  oxygen,  and  nitrogen,  and 
many  of  them  give  off  ammonia  when  heated.  Similarly^ 
compounds  containing  carbon,  oxygen,  and  hydrogen, 
even  though  they  are  thoroughly  dry,  when  heated  give 
off  oxygen  in  combination  with  hydrogen  in  the  form  of 
water.  Some  animal  substances  give  off  ammonia  when 
they  undergo  decomposition  in  the  air.  The  coal  which 
is  used  for  making  illuminating-gas  contains  some  hy- 
drogen and  nitrogen  in  chemical  combination,  and  when 
the  coal  is  heated  ammonia  is  given  off. 

143 


144  INTRODUCTION    TO   CHEMISTRY. 

Compounds  of  metals  with  nitrogen,  called  nitrides, 
give  ammonia  when  acted  upon  by  steam. 

When  animal  substances  undergo  decomposition  in  the 
presence  of  a  base  where  the  temperature  is  comparatively 
high,  the  nitrogen  combines  with  oxygen  and  the  metal 
of  the  base.  Either  a  nitrite  or  a  nitrate  is  formed;  that 
is  to  say,  either  a  salt  of~nitrous  acid,  HTs  02 ,  or  of  nitric 
acid,  HN03.  In  some  countries  where  the  conditions  are 
favorable  to  the  process,  immense  quantities  of  nitrates  are 
found,  chiefly  potassium  nitrate,  or  saltpetre,  KN03,  and 
sodium  nitrate,  or  Chili  saltpetre,  NaN03.  The  change 
of  the  nitrogen  of  animal  substances  to  the  form  of  nitrates 
is  caused  by  minute  living  organisms.  How  they  effect 
the  change  is  not  known.  From  the  salts  of  nitric  acid 
which  are  found  in  nature,  nitric  acid  itself  can  easily  be 
prepared. 

Nearly  all  the  compounds  of.  nitrogen  with  which  we 
shall  have  to  deal  are  made  either  from  ammonia  or  from 
nitric  acid. 

Ammonia,  NH3. — The  conditions  under  which  ammonia 
is  formed  have  been  mentioned.  The  chief  source  in  some 
countries  is  the  "  ammonia-water  "  of  the  gas-works.  This 
is  the  water  through  which  the  gas  has  been  passed  for  the 
purpose  of  removing  the  ammonia,  which  passes  into  solu- 
tion. By  adding  hydrochloric  acid  to  this  liquid,  am- 
monium chloride,  which  is  a  compound  of  the  acid  with 
ammonia,  is  formed.  This  is  the  well-known  substance 
sal  ammoniac.  It  appears  that  this  name  had  its  origin  in 
the  fact  that  common  salt  was  formerly  called  sal  armenia. 
cum,  and  that  afterward,  through  a  misunderstanding, 
ammonium  chloride  came  to  be  known  by  the  same  name 
which  underwent  change  to  the  form  sal  ammoniacum,  or 
sal  ammoniac.  Large  quantities  of  ammonia  are  made  by 
distilling  waste  animal  products. 


PREPARATION  OF  AMMONIA.  M5 

As  ammonium  chloride,  or  sal  ammoniac,  is  the  most 
common  compound  containing  ammonia,  it  is  used  in  the 
laboratory  for  making  ammonia.  For  this  purpose  it  is 
only  necessary  to  treat  the  salt  with  an  alkali. 

EXPERIMENT  69. — To  a  little  ammonium  chloride  on  a  watch- 
glass  add  a  few  drops  of  a  strong  solution  of  caustic  soda,  and 
notice  the  odor  of  the  gas  given  off.  Do  the  same  thing  with 
caustic  potash.  Mix  small  quantities  of  ammonium  chloride  and 
lime  in  a  mortar  and  notice  the  odor.  Has  the  ammonium  chlo- 
ride itself  this  gdor  ? 

Preparation  of  Ammonia. — Ammonia  is  best  prepared 
by  mixing  slaked  lime  and  ammonium  chloride. 

In  addition  to  the  ammonia,  which  is  given  off  in  the 
fform  of  gas,  calcium  chloride,  CaCl2,  and  water  are  formed 
in  this  reaction.  It  is  represented  thus : 

2NH4C1  +  Ca(OH),  =  2NH3  +  CaCl2  +  2H20. 

This  curious  reaction  will  be  more  fully  discussed  after 
ammonia  has  been  studied. 

EXPERIMENT  70. — Arrange  an  apparatus  as  shown  in  Fig.  30, 
p.  Ill,  omitting,  however,  the  funnel-tube  ;  a  cork  with  one 
opening  will  therefore  suffice.  Weigh  100  grams  quick-lime  into 
a  dish,  and  bring  this  into  the  flask.  Add  just  enough  water  to 
slake  it  without  making  it  moist,  then  add  50  grams  ammonium 
chloride  and  mix  by  shaking.  Push  the  stopper 
into  place  and  gently  heat  the  flask,  which  rests 
upon  a  sand-bath.  After  the  air  is  driven  out, 
the  gas  will  be  completely  absorbed  by  the 
water  in  the  first  Woulff's  flask.  Disconnect 
the  delivery-tube  from  the  Woulff's  flasks,  and 
connect  with  another  tube  bent  upward.  Collect 
some  of  the  escaping  gas  by  displacement  of  air, 
placing  the  vessel  with  the  mouth  downward,  as 
the  gas  is  much  lighter  than  air.  The  arrange- 
ment is  shown  in  Fig.  36.  The  vessel  in  which 

F IG.  36. 

the  gas  is  collected  should  be  dry,  as  water  ab- 
sorbs ammonia  very  readily.     Hence,  also,  it  cannot  be  collected 


146  INTRODUCTION    TO   CHEMISTRY. 

over  water.  In  the  gas  collected  introduce  a  burning  stick  or 
taper.  Ammonia  does  not  burn  in  air,  nor  does  it  support  com- 
bustion. In  working  with  the  gas  great  care  must  be  taken 
to  avoid  inhaling  it  in  any  quantity.  After  enough  has  been 
collected  in  cylinders  to  exhibit  the  chief  properties,  connect 
the  delivery-tube  again  with  the  Woulff's  flasks,  and  pass  the 
gas  over  the  water  as  long  as  it  is  given  off. 

Properties  of  Ammonia. — From  the  observations  made 
in  the  experiments  just  performed,  it  is  seen  that  ammonia 
is  a  colorless,  transparent  gas.  It  has  a  very  penetrat- 
ing characteristic  odor.  In  concentrated  form  it  causes 
suffocation.  Its  specific  gravity  is  0.59;  that  is  to  say, 
it  is  but  little  more  than  half  as  heavy  as  air.  It  can 
easily  be  reduced  to  the  liquid  form  by  pressure  and  cold. 
When  the  pressure  is  removed  from  the  liquefied  am- 
monia, it  passes  back  to  the  form  of  gas.  In  so  doing  it 
absorbs  heat.  These  facts  are  taken  advantage  of  in  the 
artificial  preparation  of  ice,  as  by  means  of  Carre's  ice- 
machine. 

Ammonia  does  not  burn  in  the  air,  but  does  burn  in 
oxygen.  It  is  absorbed  by  water  in  very  large  quantity. 
One  volume  of  water  at  the  ordinary  temperature  dissolves 
about  600  volumes  of  ammonia-gas,  and  at  0°  about  1000 
volumes. 

[PROBLEM. — A  litre  of  air  at  0°  weighing  1.293  grams,  and  the 
specific  gravity  of  ammonia  gas  being  0.59,  how  much  would,  a 
litre  of  water  increase  in  weight  by  being  saturated^with  am- 
monia at  0°  ?] 

The  solution  of  ammonia  in  water  is  what  is  generally 
called  ammonia  in  the  laboratory.  It  was  formerly  called 
"  spirits  of  hartshorn."  The  solution  has  the  odor  of  the 
gas.  It  loses  all  its  gas  when  boiled  for  some  time.  The 
solution  shows  a  strong  alkaline  reaction  and  has  the  power 
to  neutralize  acids. 


SAL TS    FORMED  BY  AMMONIA.  14? 

EXPERIMENT  71. — Put  100  cc.  of  a  dilute  solution  of  ammonia 
in  an  cvaporating-dish.  Try  its  effect  on  red  litmus  paper. 
Slowly  add  dilute  hydrochloric  acid  until  the  alkaline  reaction 
is  destroyed  and  the  solution  is  neutral.  Evaporate  to  dryness 
on  a  water-bath.  Compare  the  substance  thus  obtained  with  sal 
ammoniac  or  ammonium  chloride.  Taste  them.  Heat  them  on 
a  piece  of  platinum-foil.  Treat  them  with  a  caustic  alkali. 
Treat  with  a  little  concentrated  sulphuric  acid  in  dry  test-tubes. 
Do  they  appear  to  be  identical  ? — The  product  is  ammonium 
chloride,  NH4C1.  Similarly  sulphuric  acid  and  ammonia  yield 
ammonium  sulphate  ;  nitric  acid  and  ammonia  yield  ammonium 
nitrate,  etc. 

EXPERIMENT  72. — Fill  a  cylinder  with  ammonia-gas,  and  an- 
other of  the  same  size  with  hydrochloric-acid  gas.  Bring  them 
together  with  their  mouths  covered.  Quickly  remove  the  covers, 
when  a  dense  white  cloud  will  appear  in  and  about  the  cylinders. 
This  will  soon  settle  on  the  walls  of  the  vessels  as  a  light  white 
solid.  It  is  ammonium  chloride.  Thus,  from  two  colorless  gases 
a  solid  substance  is  obtained  by  an  act  of  chemical  combination. 
Heat  is  evolved  in  the  act  of  combination. 


Salts  Formed  by  Ammonia. — It  has  been  shown  that  the 
alkalies  are  strong  bases,  and  that  hages  are  compounds  of 
metals  with  hydrogen  and  oxygen.  Certainly  those  sub- 
stances which  show  an  alkaline  reaction  are  compounds  of 
metals. with  hydrog'eii  and  oxygen,  and  the  alkaline  reaction 
and  basic  properties  are  believed  to  be  due  to  the  hydroxyl, 
OH.  But  in  the  solution  of  ammonia  in  water  we  have 
a  substance  which  shows  an  alkaline  reaction  and  acts 
in  nearly  all  respects  much  like  a  solution  of  sodium 
hydroxide  or  potassium  hydroxide.  The  salts  which 
ammonia  forms  with  acids  are  similar  to  the  salts  of 
sodium  and  potassium.  What  is  the  substance  that  has 
the  alkaline  reaction  ?  and  what  are  the  salts  that  are 
formed  by  the  action  of  acids  on  ammonia  ?  In  the  first 
place,  it  has  been  found  that  when  an  acid  acts  on 
ammonia  the  two  combine  directly  without  the  formation 


148  INTRODUCTION    TO   CHEMISTRY. 

of  anything  but  the  salt.     Thus  ammonia  and  hydrochloric 
acid  form  ammonium  chloride: 


NH8  +  IIC1  =  NH4C1. 

Ammonia  and  nitric  acid  form  ammonium  nitrate  : 
NH3  +  HJST03  =  NH4NOS  ,     etc.,  etc. 

Ammonium  Theory.  —  On  comparing  the  formulas  of 
ammonium  salts  with  those  of  potassium  and  sodium  salts 
*  it  will  he  seen  that,  while  in  the  potassium  and  sodium 
salts  the  metals  potassium  and  sodium  take  the  place  of 
the  hydrogen  of  the  acids,  in  the  ammonium  salts  the 
place  of  the  hydrogen  of  the  acid  is  taken  hy  a  compound 
of  the  formula  NII4.  It  has  been,  suggested,  and  the  idea 
has  been  generally  accepted,  that  when  ammonia-gas  dis- 
solves in  water  the  ions  N"II4  and  OH  of  an  unstable  com- 
pound of  the  formula  NH4OH  are  formed  thus  : 

Nil,  +  H20  =  NH4OH(=  NH4  -f  OH). 

In  this  hydroxide,  as  in  the  salts  of  ammonia,  the  group 
or  ion  NH4  appears  to  play  the  part  of  a  metal  ion.  The 
group  NH4  is,  however,  wholly  hypothetical.  As  it 
appears  to  be  this  which  plays  the  part  of  a  metal  in  the 
solution  as  well  .as  in  the  salts,  the  name  ammonium  has 
been  given  to  it,  the  ending  ium  being  that  which  is  usually 
given  to  signify  metallic  character.  We  speak,  then,  of 
ammonium  salts,  just  as  we  speak  of  potassium  or  sodium 
or  calcium  salts.  In  the  ammonium  salts  the  hypothetical 
compound  metal  ammonium,  NH4,  is  assumed  to  be 
present.  If,  however,  we  attempt  to  set  it  free  or  to  set 
its  hydroxide  free,  we  get  ammonia.  On  treating  am- 
monium chloride  with  lime,  if  any  action  takes  place  at 


COMPOSITION  OF  AMMONIA  BY   WEIGHT.          149 

all,  we  should  expect  it  to  be  that  represented  by  the  equa 
tion 

2NH4C1  +  Ca(OH),  =  CaCl2  +  2NH4OH; 

that  is  to  say,  we  should  expect  the  calcium  and  ammonium 
to  exchange  places.  Perhaps  this  is  the  action  that  takes 
place  at  first.  But  the  compound  NH4OH,  or  ammonium 
hydroxide,  if  formed  at  all,  breaks  up  at  once  into  ammonia 
and  water,  thus  : 


NH4OH  =  NH3  +  H20. 

So,  too,  if  ammonium  hydroxide,  NH4OH,  and  its  ions 
4  and  OH,  are  present  in  the  solution  of  ammonia  in 
water,  a  rearrangement  takes  place  very  readily  and 
ammonia  and  water  are  formed  under  the  influence  of 
gentle  heat,  and  ammonia-gas  is  given  off. 

Composition  of  Ammonia  by  Weight.  —  By  oxidation 
under  the  proper  conditions  it  is  possible  to  convert  the 
hydrogen  of  ammonia  into  water  and  leave  the  nitrogen  in 
the  free  state.  As  water  and  nitrogen  are  the  only 
products  formed,  and  the  quantity  of  oxygen  used  up  in 
the  oxidation  is  equal  to  the  quantity  of  oxygen  found  in 
the  water  formed,  it  follows  that  nitrogen  and  hydrogen 
are  the  only  elements  contained  in  ammonia. 

When  electric  sparks  are  passed  for  some  time  through 
a  mixture  of  nitrogen  and  hydrogen,  some  ammonia  is 
formed.  Conversely,  when  electric  sparks  are  passed  for 
a  time  through  ammonia,  nitrogen  and  hydrogen  are 
obtained. 

If,  in  the  oxidation  of  a  kiiownjauantity  of  ammonia, 
the  water  formed  and  tra  nitrogen  left  uncombined  are 
accurately  determined,  it  will  be  found  that  in  ammonia 
the  elements  are  combined  in  the  proportion  of  fourteen 


15°  INTRODUCTION   TO   CHEMISTRY. 

parts  hy  weight  of  nitrogen  to  three  parts  hy  weight  of 
hydrogen.  This  fact  is  expressed  by  the  formula  NH3; 
14.04  being  the  atomic  weight  of  nitrogen. 

Composition  of  Ammonia  by  Volume. — The  proportion 
by  volume  in  which  the  two  elements  combine  may  be 
determined  by  the  following  method.  When  ammonia  is 
treated  with  chlorine  it  is  decomposed,  the  chlorine  com- 
bining with  hydrogen,  and  the  nitrogen  being  left  uncom- 
bined.  The  reaction  is  represented  thus : 

NH8  +  3C1  =  N"  +  3HC1. 

Hydrogen  and  chlorine  unite  in  equal  volumes,  as  has 
already  been  seen.  Now,  if  a  solution  of  ammonia  is 
added  to  a  measured  volume  of  chlorine  until  the  chlorine 
is  all  used  up,  the  volume  of  hydrogen  which  is  extracted 
from  ammonia  is  equal  to  the  volume  of  chlorine  used. 
The  nitrogen  left  over  was  combined  with  the  hydrogen 
whose  volume  has  already  been  determined.  It  would  be 
found  that  the  volume  of  nitrogen  is  to  that  of  the 
hydrogen  with  which  it  was  combined  as  1  to  3;  or  in 
ammonia  1  volume  of  nitrogen  is  combined  with  3  volumes 
of  hydrogen. 

When  a  given  volume  of  ammonia  is  decomposed  into 
nitrogen  and  hydrogen,  the  mixture  occupies  just  twice 
the  volume  that  the  ammonia  did;  or,  if  nitrogen  and 
hydrogen  in  the  proper  proportions  to  form  ammonia 
are  caused  to  combine,  the  ammonia  formed  occupies 
one  half  the  volume  occupied  by  the  mixture  of  the  two 


Relations  between  the  Volumes  of  Combining  Gases.— 

In  studying  the  volume-relations  of  hydrogen,   chlorine, 
and  hydrochloric  acid  with  reference  to  one  another,  we 


VOLUMES   OF  COMBINING   GASES. 


found  that  when  hydrogen  and  chlorine  combine  one 
volume  of  the  one  combines  with  one  volume  of  the  other, 
and  two  volumes  of  the  product  are  formed.  These  facts 
may  be  represented  graphically  thus : 


and         combine  to  form 


2   volumes    hy- 
drochloric acid. 


When  hydrogen  and  oxygen  combine,  two  volumes  of 
hydrogen  combine  with  one  volume  of  oxygen;  and  the 
three  volumes  of  gas  thus  combined  form  two  volumes  of 
water- vapor : 

2  volumes  hydrogen 


and     combine  to  form 


2  volumes 
water-vapor. 


Finally,  it  has  just  "been  shown  that  one  volume  of 
nitrogen  combines  with  three  volumes  of  hydrogen  to  form 
two  volumes  of  ammonia : 


152  INTRODUCTION    TO   CHEMISTRY. 

3  volumes  hydrogen 


and 


combine  to  form 


2  volumes 
ammonia. 


Gay  Lussac's  Law  of  Volumes. — A  careful  study  of  the 
volumes  of  combining  gases  has  shown  that  these  volumes 
always  hear  a  simple  relation  to  one  another  and  to  the 
volumes  of  the  products  formed.  The  three  cases  above 
presented  show  the  more  common  relations  met  with 
among  the  elements. 

Condensation  or  Contraction. — It  is  clear  that  the  three 
elements  chlorine,  oxygen,  and  nitrogen  influence  hy- 
drogen differently.  One  volume  of  chlorine  can  hold  in 
combination  but  one  volume  of  hydrogen.  One  volume 
of  oxygen  can  hold  in  combination  two  volumes  of 
hydrogen,  and  at  the  same  time  it  causes  a  condensation  of 
volume  from  three  volumes  of  gas  to  two.  One  volume  of 
nitrogen  can  hold  in  combination  three  volumes  of 
hydrogen,  and  at  the  same  time  it  causes  a  condensation 
of  four  volumes  of  gas  to  two.  Nothing  is  known  regard- 
ing the  cause  of  this  contraction  of  volume. 

Relations  between  the  Specific  Gravities  of  Gases  and 
their  Atomic  Weights. — Attention  has  already  been  called 
to  the  fact  that  the  weights  of  equal  volumes  of  hydrogen, 
chlorine,  and  oxygen  stand  in  the  same  relation  to  one 
another  as  the  combining  weights.  Nitrogen  is  no  excep- 


SPECIFIC   GRAVITIES,  ETC,   OP  GASES.  153 

tion  to  this  rule.  The  specific  gravity  of  nitrogen  is 
0.967.  One  litre  of  nitrogen  weighs  1.2507  grams.  The 
specific  gravity  of  hydrogen  is  0.0606;  and  the  weight  of 
a  litre  of  hydrogen  is  0.08995.  But  0.0696  :  0.967  : :  1  :  14 
and,  of  course,  0.08995:1.2507::!  :  14.  The  accepted 
combining  weight  of  nitrogen  is  14. 

These  remarkable  facts  may  be  represented  graphically 
thus : 


11 

w 

itre  of  hydrogen      1  litre  of  chlorine       1  litre  of  oxygen         1  litre  of  nitrog 
iighs  0.08995  gr.         weighs  3.22  gr.           weighs  1.429  gr.           weighs  1.2507  £ 

These  figures  bear  to  one  another  very  nearly  the  rela- 
tions expressed  by  the  figures  1,  35.4,  16,  and  14.  But 
these  last  figures  very  nearly  express  the  atomic  weights 
of  the  elements.  It  appears,  therefore,  that  the  atomic 
weights  of  some  of  the  gaseous  elements  bear  to  one  another 
the  same  relations  as  the  iveights  of  equal  volumes  of  the 
gases. 

Observations  of  this  kind,  together  with  other  observa- 
tions on  the  conduct  of  gases,  have  led  to  a  very  important 
conception  in  regard  to  the  nature  of  gases  and  the  consti- 
tution of  matter.  This  will  be  treated  of  farther  on.  For 
the  present  it  will  be  best  to  keep  to  the  facts,  so  that 
before  taking  up  speculations  in  regard  to  the  hidden 
causes  of  the  phenomena  observed  we  may  gain  a  solid 
foundation  for  these  speculations.  It  should  also  be  borne 
in  mind  that  the  object  of  speculation  is  not  to  devise 
theories  for  their  own  sake,  but  to  help  us  to  understand 
the  facts,  and  to  lead  to  further  discovery  of  facts. 

Nitric  Acid,  HN03. — To  effect  the  direct  union  of 
nitrogen  with  oxygen  and  hydrogen  is  not  easier  than  to 


154  INTRODUCTION   TO   CHEMISTRY. 

effect  the  direct  union  of  nitrogen  with  hydrogen  to  form 
ammonia.  Nevertheless,  the  silent  and  continuous  action 
of  minute  organisms  in  the  soil  is  always  tending  to  trans- 
form the  waste-products  of  animal  life  into  compounds 
closely  allied  to  nitric  acid.  The  process  of  nitrification 
has  already  been  referred  to.  It  is  plainly  an  oxidizing 
process.  In  general,  by  oxidation  the  nitrogen  of  animal 
substances  is  converted  into  nitric  acid,  while  by  reduction 
it  is  converted  into  ammonia. 

Preparation  of  Nitric  Acid.  —  In  preparing  nitric  acid  a 
nitrate  is  always  used  as  the  starting-point,  and  in  this  the 
hydrogen  is  substituted  for  the  metal.  This  is  done  in  the 
same  way  that  hydrogen  is  substituted  for  the  metal 
sodium  in  sodium  chloride  in  the  preparation  of  hydro- 
chloric acid,  —  viz.,  by  treating  the  salt  with  some  acid: 

H2S04  =  Na,S04  +  2HC1; 


In  these  cases  the  acids  obtained  are  volatile  under  the 
conditions  of  the  experiment.  Acids  that  are  not  volatile 
under  the  conditions  of  the  experiment  decompose  the  salts 
of  those  that  are.  At  a  sufficiently  high  temperature  sul- 
phuric acid  is  volatile,  and  an  acid  that  is  not  volatile 
at  such  a  temperature  will  set  sulphuric  acid  free. 

EXPERIMENT  73.  —  Arrange  an  apparatus  as  shown  in  Fig.  37. 
In  the  retort  put  40  grams  sodium  nitrate  (Chili  saltpetre)  and 
20  grams  concentrated  sulphuric  acid.  On  gently  heating,  nitric 
acid  will  distil  over,  and  be  condensed  in  the  receiver.  After 
the  acid  is  all  distilled  off,  remove  the  contents  of  the  retort.  Re- 
crystallize  the  substance  from  water,  and  compare  it  with  the 
sodium  sulphate  obtained  in  the  preparation  of  hydrochloric  acid. 
(See  Experiment  57.)  In  the  latter  stage  of  the  operation  the 
vessels  become  filled  with  a  reddish-brown  gas.  The  acid  which 
is  collected  has  a  somewhat  yellowish  color. 


NITRIC  ACID. 


'55 


Pure  nitric  acid  is  a  colorless  liquid.  It  gives  off  color- 
less fumes  when  exposed  to  the  air.  When  boiled  it 
undergoes  slight  decomposition  into  oxygen,  water,  and 
compounds  of  nitrogen  and  oxygen.  One  of  these  com- 
pounds is  colored,  and  it  is  this  that  is  noticed  in  the 
above  experiment,,  and  whenever  strong  nitric  acid  is 


FIG.  37. 

boiled.  Nitric  acid  undergoes  a  similar  decomposition 
when  exposed  to  the  action  of  the  direct  rays  of  the  sun. 
In  consequence  of  this  decomposition  bottles  containing 
strong  nitric  acid  always  contain  a  reddish-brown  gas  above 
the  liquid  after  standing  for  some  time.  It  acts  violently 
on  a  great  many  substances,  disintegrating  them.  It 
causes  bad  wounds  in  contact  with  the  flesh :  eats  through 
clothing;  burns  wood;  dissolves  metals;  and  is  altogether 
one  of  the  most  active  of  chemical  substances.  In  work- 
ing with  the  concentrated  acid  it  is  necessary  to  exercise 
the  greatest  care. 

Commercial  nitric  acid  contains  only  about  G8  per  cent 
of  the  chemical   compound   HN03.     The  rest  is  mostly 


156  INTRODUCTION    TO  CHEMISTRY. 

water,  though  there  are  several  impurities  present  in  small 
quantity.  In  order  to  get  concentrated  pure  acid  from 
this  it  must  be  distilled  after  the  addition  of  some  concen- 
trated sulphuric  acid. 

EXPERIMENT  74. — Mix  200  grams  concentrated  sulphuric  acid 
and  100  grams  ordinary  concentrated  nitric  acid.  Pour  the  sul- 
phuric acid  into  the  nitric  acid.  Distil  the  mixture  very  slowly 
from  a  retort  arranged  as  in  Experiment  73,  taking  care  to  keep 
the  neck  of  the  retort  cool  by  placing  filter-paper  moistened  with 
cold  water  on  it.  Use  the  acid  thus  obtained  for  the  purpose  of 
studying  the  properties  of  pure  nitric  acid.  N.  B.  The  substance 
is  dangerous,  and  these  experiments  require  great  caution  ! 

Nitric  Acid  an  Oxidizing  Agent. — In  consequence  of  the 
ease  with  which  nitric  acid  decomposes,  giving  up  oxygen, 
it  is  an  excellent  oxidizing  agent,  and  is  much  used  in  the 
laboratory  in  this  capacity.  The  following  experiments 
illustrate  this  action : 

EXPERIMENT  75. — See  Note  at  the  end  of  Experiment  74.— Pour 
some  fuming  nitric  acid  into  a  wide  test-tube,  so  that  it  is  about 
one  fourth  filled.  Heat  the  end  of  a  stick  of  charcoal  of  proper 
size,  and,  holding  the  other  end  with  a  forceps,  introduce  the 
heated  end  into  the  acid. — It  will  continue  to  burn  with  a  bright 
light,  even  though  it  is  placed  below  the  surface  of  the  liquid. 
The  action  is  oxidation.  The  charcoal  in  this  case  finds  the 
oxygen  in  the  acid,  and  not  in  the  air.  Great  care  must  be 
taken  in  performing  this  experiment.  The  charcoal  should  not 
come  in  contact  with  the  sides  of  the  test-tube.  A  large  beaker- 
glass  should  be  placed  beneath  the  test-tube,  so  that,  in  case  it 
should  break,  the  acid  will  be  caught  and  prevented  from  doing 
harm.  The  arrangement  of  the  apparatus  is  shown  in  Fig.  38. 

The  gases  given  off  from  the  tube  are  offensive  and  poisonous. 
Hence  this  as  well  as  all  other  experiments  with  nitric  acid  should 
be  carried  on  under  a  hood  in  which  there  is  a  good  draught. 

EXPERIMENT  76.— Boil  a  little  fuming  nitric  acid  in  a  test-tube 
in  the  upper  part  of  which  some  woolen  yarn  has  been  introduced 
in  the  form  of  a  stopper.  The  woolen  yarn  will  take  fire  and 
burn,  leaving  a  white  residue.  Hold  the  test-tube  with  a  forceps 
over  a  vessel  to  catch  the  contents  should  the  tube  break. 


ACTION  OF  NITRIC  ACID  ON  METALS.  157 

EXPERIMENT  77. —In  a  small  flask  put  a  few  pieces  of  granu- 
lated tin.  Pour  on  this  just  enough  ordinary  concentrated  nitric 
acid  to  cover  it.  Heat  gently  over  a  small  flame.  Soon  action 


FIG.  38. 

will  take  place.  Colored  gases  will  be  evolved,  the  tin  will  dis- 
appear, and  in  its  place  will  be  found  a  white  powder.  This  con- 
sists mostly  of  tin  and  oxygen.  (See  Experiment  15.) 

Action  of  Nitric  Acid  on  Metals. — Like  other  acids, 
nitric  acid  forms  salts  with  the  metals.  These  can  be 
made  by  treating  the  metals  themselves  with  the  acid,  but 
in  this  case  the  formation  of  the  salt  is  accompanied  by 
another  kind  of  action  which  is  quite  characteristic  of 
nitric  acid.  The  acid  gives  up  a  part  of  its  oxygen  and  is 
thus  converted  into  compounds  of  oxygen  and  nitrogen 
which  contain  a  smaller  proportion  of  oxygen  than  the 
acid.  The  compound  most  commonly  formed  in  this  way 
is  nitric  oxide,  NO.  It  appears  probable  that  the  metal 
first  abstracts  oxygen  from  the  acid,  and  that  the  oxide 
thus  formed  then  dissolves  in  a  part  of  the  acid  as  the 
nitrate.  The  action  in  the  case  of  copper  should,  accord- 
ing to  this,  be  represented  as  taking  place  in  two  stages. 


I58  INTRODUCTION   TO  CHEMISTRY. 

First,  nitric  oxide,  water,  and  copper  oxide  are  formed  as 
represented  in  this  equation : 

(1)  2HN08  +  3Cu  =  H20  +  3GuO  +  2ND. 

Then  the  copper  oxide  forms  copper  nitrate  with  some  of 
the  acid,  and  this  nitrate  dissolves : 

(2)  CuO  -f  2HN03  =  Cu(N03)2  +  H20. 

It  is  possible  that  to  some  extent  hydrogen  is  set  free 
from  the  acid  by  the  action  of  the  metal,  and  that  this  acts 
upon  the  acid,  reducing  it  to  lower  oxides  of  nitrogen. 
Nitric  oxide,  NO,  unites  with  oxygen  from  the  air,  and 
forms  nitrogen  peroxide,  N02,  a  colored  gas,  which  is 
always  seen  when  nitric  acid  acts  upon  metals. 

EXPERIMENT  78.— Dissolve  a  few  pieces  of  copper-foil  in  ordi- 
nary commercial  nitric  acid  diluted  with  about  half  its  volume  of 
water.  The  operation  should  be  carried  on  in  a  good-sized  flask 
and  under  an  efficient  hood.  When  the  copper  has  disappeared, 
pour  the  blue  solution  into  an  evaporating-dish,  and  evaporate 
down  to  crystallization.  Compare  the  substance  thus  obtained 
with  copper  nitrate. — Heat  a  specimen  of  each. — Treat  small 
specimens  with  sulphuric  acid. — Do  the  two  substances  appear  to 
be  identical  ? 

EXPERIMENT  79. — Heat  specimens  of  potassium  nitrate,  sodium 
nitrate,  lead  nitrate,  and  any  other  nitrates  that  may  be  avail- 
able. All  are  decomposed,  giving  off  oxygen,  in  some  cases 
mixed  with  oxides  of  nitrogen,  among  which  is  nitrogen  peroxide, 
which  can  be  recognized  by  its  color. 

General  Properties  of  the  Salts  of  Nitric  Acid. — All 
salts  of  nitric  acid  are  decomposed  by  heat,  and  all  are 
soluble  in  water. 

EXPERIMENT  80. — Try  the  solubility  in  water  of  the  nitrates 
used  in  the  last  experiment. 

Ammonia  Formed  by  Reduction  of  Nitric  Acid. — The 
formation  of  ammonia  by  reduction  of  nitric  acid  may  be 
shown  by  the  following  experiment. 


AQUA  REG1A— NITROUS  ACID.  159 

EXPERIMENT  81. — In  a  good-sized  test-tube  treat  a  few  pieces 
of  granulated  zinc  with  dilute  sulphuric  acid.  What  is  evolved  ? 
Now  add  drop  by  drop  dilute  nitric  acid.  Pour  the  contents  of 
the  tube  into  an  evaporating-dish  and  evaporate  the  liquid.  Put 
the  residue  into  a  test-tube  and  add  a  solution  of  caustic  soda. 
What  is  given  off  ?  Try  the  action  of  the  gas  on  red  litmus  paper. 
Moisten  the  end  of  a  glass  rod  with  a  little  hydrochloric  acid  and 
hold  it  in  the  tube.  What  do  you  observe  ?  Explain  it.  Do  the 
same  with  nitric  acid.  What  are  the  fumes  in  this  case  ? 

Aqua  Regia. — Aqua  regia  is  made  by  mixing  together 
concentrated  nitric  and  hydrochloric  acids.  It  received 
its  name  for  the  reason  that  it  can  dissolve  gold,  the  king 
of  metals.  It  is  an  excellent  solvent,  and  is  much  used  in 
the  laboratory. 

Nitrous  Acid,  HN02. — Among  the  reduction-products 
of  nitric  acid  is  nitrous  acid,  HN02.  A  salt  of  this  acid 
is  most  easily  prepared  by  reducing  a  nitrate.  Thus,  if 
potassium  nitrate,  KN03 ,  is  melted  together  with  metallic 
lead,  the  lead  extracts  a  part  of  the  oxygen  and  leaves 
potassium  nitrite,  KN02: 

KN03  +  Pb  =  KN02  +  PbO. 

EXPERIMENT  82. — Heat  together  in  a  shallow  iron  pan  25  grams 
potassium  nitrate  and  about  50  grams  metallic  lead.  When 
both  are  melted  stir  them  together  as  thoroughly  as  possible. 
After  the  mass  is  cooled  down,  break  it  up  and  treat  with  a  little 
warm  water.  The  potassium  nitrite  will  dissolve,  while  the  lead 
oxide  add  lead  will  not.  Filter.  Add  a  little  sulphuric  acid  to 
some  of  the  solution.  What  is  given  off  ?  See  whether  a  solu- 
tion of  potassium  nitrate  acts  in  the  same  way. 

Nitrous  Acid  breaks  down  into  Nitrogen  Trioxide  and 
Water. — When  an  acid  is  added  to  a  solution  of  a  nitrite, 
the  salt  is  decomposed  and  nitrogen  trioxide  or  nitrous 
anhydride,  N203,  is  given  off.  Were  the  action  in  this 
case  analogous  to  that  which  takes  place  when  sulphuric 


160  INTRODUCTION   TO  CHEMISTRY. 

acid  acts  upon  a  nitrate  or  upon  a  chloride,  it  would  be 
represented  thus : 

2KN02  -j-  H2S04  =  K2SO,  -f  21IN02. 

Nitrous  acid  would  be  formed;  but  instead  of  this  a  sub- 
stance which  is  nitrous  acid  minus  the  elements  of  water 
is  formed: 

2HN02  =  N203  -f  H,0. 

This  tendency  on  the  part  of  compounds  containing 
hydrogen  and  oxygen  to  decompose  with  formation  of 
water  is  very  commonly  observed.  We  have  already  had 
to  deal  with  a  case  of  the  kind  in  ammonium  hydroxide. 
This  substance,  which  probably  exists  in  solution  in  water, 
yields  ammonia  and  water  when  heated.  Many  compounds 
that  do  not  break  up  in  this  way  at  ordinary  temperatures 
do  so  at  elevated  temperatures.  This  decomposition  is  to 
be  ascribed  to  the  strong  tendency  of  hydrogen  to  combine 
with  oxygen.  In  complex  compounds  several  forces  are 
at  work  to  keep  the  constituents  in  equilibrium.  If  the 
attraction  of  hydrogen  for  oxygen  is  much  stronger  than 
the  other  forces  at  work,  the  equilibrium  is  disturbed,  and 
decomposition  takes  place.  At  least,  this  is  the  thought 
that  naturally  suggests  itself  by  way  of  partial  explanation 
of  the  phenomenon. 

Anhydrides, — A  compound  which,  in  its  composition, 
bears  to  an  acid  the  relation  that  nitrogen  trioxide,  N203 , 
bears  to  nitrous  acid,  HN02.  is  called  an  anhydride. 
Thus  we  have  nitrous  anhydride,  N203;  nitric  anhydride, 
N205,  etc.  Nitric  anhydride  bears  the  same  relation  to 
.nitric  acid  that  nitrous  anhydride  bears  to  nitrous  acid: 

N203  +  H20  = 
N206  +  H20  = 


THE  OXIDES  OF  NITROGEN.  161 

In  more  general  terms,  it  may  be  said  that  any  oxide 
which,  when  brought  together  with  water,  forms  an  acid 
by  direct  combination,  is  an  anhydride.  Other  examples 
of  this  class  of  compounds  will  be  met  with  farther  on. 

The  Oxides  of  Nitrogen, — Nitrogen  and  oxygen  form 
five  compounds  with  each  other,  of  which  all  but  one  have 
already  been  mentioned.  The  names  and  formulas  of  the 
five  compounds  are  nitrogen  peroxide,  N02;  nitric  oxide, 
NO;  nitrous  oxide,  N20;  nitrous  anhydride,  N203;  and 
nitric  anhydride,  N205.  If  the  formulas  of  these  com- 
pounds are  arranged  in  a  series,  beginning  with  that  one 
which  contains  the  smallest  proportion  of  oxygen,  it  will 
be  seen  that  the  series  affords  a  striking  illustration  of  the 
facts  from  which  the  law  of  multiple  proportions  is 
deduced.  The  series  is : 

Nitrous  oxide N20 

Nitric  oxide NO  or  N202 

Nitrogen  trioxide N203 

Nitrogen  peroxide N02  or  N204 

Nitric  anhydride.'.'.' N205 

It  will  be  seen  that  the  weights  of  oxygen  combined 
with  28  parts  by  weight  of  nitrogen  are  16,  32,  48,  64, 
and  80. 

[What  other  series  of  compounds  have  we  already  had 
to  deal  with  that  illustrates  the  law  of  multiple  proportions 
almost  equally  strikingly  ?] 

Of  the  oxides  of  nitrogen,  only  three  need  be  studied 
here,  and  after  what  has  already  beeu  said  they  need  be 
studied  only  briefly. 

Nitrous  Oxide,  N20. — This  compound  is  formed  by  re- 
duction of  nitric  acid  when  the  acid  acts  upon  metals  and 
the  degree  of  concentration  and  the  temperature  are  favor- 
able. It  is  usually  prepared  by  heating  ammonium 


1 62  INTRODUCTION   TO   CHEMISTRY. 

nitrate,    NH4N03.      The   decomposition    takes    place   as 
represented  thus : 


the  products  being  nitrous  oxide  and  water.  In  this 
reaction  the  tendency  of  hydrogen  and  oxygen  to  combine 
at  elevated  temperatures  is  shown.  At  ordinary  tempera- 
tures this  tendency  is  not  strong  enough  to  cause  a  dis- 
turbance of  the  equilibrium  of  the  parts  of  the  compound. 
As  the  temperature  is  elevated  it  becomes  stronger  and 
stronger,  until  finally  the  decomposition  above  represented 
takes  place  and  the  elements  combine. 

EXPERIMENT  83.— In  a  retort,  heat  10  to  15  grams  crystallized 
ammonium  nitrate  until  it  has  the  appearance  of  boiling.  Do 
not  heat  higher  than  is  necessary  to  secure  a  regular  evolution  of 
gas.  Connect  a  wide  rubber  tube  directly  with  the  neck  of  the 
retort  and  collect  the  evolved  gas  over  water,  as  in  the  case  of 
oxygen.  It  supports  combustion  almost  as  well  as  pure  oxygen. 
Try  experiments  with  wood,  a  candle,  and  a  piece  of  phosphorus 
in  a  deflagrating-spoon. 

\  Properties. — The  gas  is  colorless  and  transparent.  It 
has  a  slightly  sweetish  taste.  It  is  somewhat  soluble  in 
water,  so  that  when  collected  over  water  there  is  always 
considerable  loss.  When  inhaled  it  causes  a  kind  of  in- 
toxication, which  is  apt  to  show  itself  in  the  form  of 
hysterical  laughing,  hence  the  name  laughing-gas.  Inhaled 
in  larger  quantity  it  causes  unconsciousness  and  insen- 
sibility to  pain.  It  is  therefore  used  to  prevent  pain  in 
minor  surgical  operations,  as,  for  example,  in  pulling 
teeth. 

Nitrous  oxide  is  easily  converted  into  a  liquid  by  cold 
and  pressure.  In  this  form  it  can  now  be  bought  con- 
tained in  strong  iron  cylinders.  On  opening  the  stop-cock 
of  the  cylinder  the  substance  escapes  in  gaseous  form. 


NITRIC  OXIDE. 


163 


Nitric  Oxide,  NO. — This  gas  is  formed  when  nitric  acid 
acts  upon  some  metals,  as  copper.  The  action  is  believed 
to  involve  two  changes,  as  described  on  p.  158. 

The  two  equations  representing  the  action  may  be  com- 
bined in  one,  thus: 

8HNO,  +  3Cu  =  3Cu(N03)2  +  4H20  +  2NO. 

As  already  stated,  however,  it  is  possible  that  to  some 
extent  the  formation  of  the  nitric  oxide  is  due  to  the  two 
reactions  represented  in  the  equations : 

3  +  Cu  =  @u(ISrts)2  +  2H,     and 

3  -f  6H  =  4H2<s)  -f  2NG. 
*  • 

EXPERIMENT  84. — Arrange  an  apparatus  as  shown  in  Fig.  39. 
In  the  flask  put  a'tfew  pieces  of  copper-foil.  7£ 
Cover  this  with  water.  Now  add  slowly, 
waiting  each  time  ror  the  action  to  begin, 
ordinary  concentrated  nitric  acid.  When 
enough  nitric  acid  has  been  added  gas  will 
be  evolved.  If  too  much  acid  is  added,  it 
not  infrequently  happens  that  the  evolution 
of  gas  takes  place  too  rapidly,  so  that  the 
liquid  is  forced  out  of  the  flask  through  the 
funnel-tube.  This  can  be  avoided  by  not 
being  in  a  hurry.  At  first  the  vessel  becomes 
filled  with  a  reddish-brown  gas,  but  soon 
the  gas  evolved  becomes  colorless.  Collect 
over  water  two  or  three  vessels  full.  The 
g  is  collected  is  principally  nitric  oxide,  NO, 
though  it  is  frequently  mixed  with  a  consid- 
erable quantity  of  nitrous  oxide. 

EXPERIMENT  85.— Turn  one  of  the  vessels 
containing  colorless  nitric    oxide   with    the  FIG.  39. 

mouth  upward  and  uncover  it.  A  colored  gas  is  at  once  seen, 
presenting  a  very  striking  appearance.  Do  not  inhale  the  gas. 
Perform  the  experiment  with  nitric  oxide' where  there  is  a  good 
draught.  Put  a  burning  splinter  of  wood  in  one  of  the  vessels 
containing  nitric  oxide.  Into  another  put  a  deflagrating-spoon 


164  INTRODUCTION    TO   CHEMISTRY. 

containing  burning  sulphur.     Burning  phosphorus  will  continue 
to  burn  in  the  gas. 

Properties  of  Nitric  Oxide. — Nitric  oxide  is  a  colorless, 
transparent  gas.  Its  most  remarkable  property  is  its 
power  to  combine  directly  with  oxygen  when  the  two  are 
brought  together.  The  act  of  combination  is  not  accom- 
panied by  the  appearance  of  light,  though  heat  is  evolved. 
The  reaction  is  represented  by  the  equation 

NO  +  0  =  N02. 

The  product  is  nitrogen  peroxide,  and  this  at  ordinary 
temperatures  is  a  reddish-brown  gas. 

Nitric  oxide  does  not  burn.  Most  burning  substances 
are  extinguished  when  introduced  into  it,  though  a  few 
when  heated  in  it  to  a  high  temperature  extract  all  or  a 
part  of  the  oxygen.  When  the  fact  is  borne  in  mind  that 
nitrous  oxide,  N20,  supports  combustion  almost  as  well  as 
oxygen,  it  appears  strange  that  another  compound  of 
nitrogen  and  oxygen,  containing  twice  as  much  oxygen 
relatively  to  the  same  quantity  of  nitrogen,  should  not 
generally  support  combustion.  This  is  explained  by  the 
relative  stability  of  the  two  compounds.  In  the  case  of 
nitrous  oxide,  the  oxygen  is  not  firmly  held  in  combina- 
tion; the  equilibrium  established  between  the  forces  at 
work  is  not  a  stable  one.  Hence,  when  a  substance  that 
readily  combines  with  oxygen  is  brought  in  contact  with, 
it,  the  equilibrium  is  disturbed,  or  the  oxide  is  decomposed. 
On  the  other  hand,  in  nitric  oxide  the  arrangement  of  the 
constituents  is  a  more  stable  one.  The  oxygen,  although 
present  in  larger  quantity  than  in  nitrous  oxide,  is  held  in 
combination  more  firmly,  and  cannot  easily  be  extracted. 
The  gas  does  not  support  combustion. 

Nitrogen  Peroxide,  N02. — This  gas  is  made  by  direct 
combination  of  nitric  oxide  with  oxygen,  as  seen  in  the 


NITROGEN  COMPOUNDS.  165 

last  experiment.  It  has  a  disagreeable  smell  and  is 
poisonous.  It  gives  up  a  part  of  its  oxygen  quite  easily, 
and  is  hence  useful  as  an  oxidizing  agent. 

Use  of  the  Oxides  of  Nitrogen  in  the  Manufacture  of 
Sulphuric  Acid. — The  higher  oxides  of  nitrogen,  especially 
the  trioxide,  N203 ,  and  the  peroxide,  N02 ,  readily  give  up 
oxygen,  and  are  changed  to  nitric  oxide,  NO.  If  air  is 
present,  nitric  oxide  is  changed  back  again  to  the  higher 
oxides,  which  may  again  give  up  oxygen,  again  yielding 
nitric  oxide,  and  so  on  indefinitely.  It  will  thus  be  seen 
that  these  oxides  of  nitrogen  may  be  made  to  serve  the 
^purpose  of  transferring  oxygen  from  the  air  to  other  sub- 
stances. Advantage  is  taken  of  these  facts  in  the  manu- 
facture of  sulphuric  acid. 

Summary. — The  simpler  nitrogen  compounds  are  made 
either  from  ammonia  or  from  nitric  acid.  Ammonia  is 
formed  in  nature  by  the  decomposition  of  animal  sub- 
stances. It  is  also  'formed  by  heating  substances  which 
contain  carbon,  hydrogen,  and  nitrogen. 

Nitric  acid  is  formed  in  nature  as  the  potassium  or 
sodium  salt,  by  the  action  of  certain  organisms  011  sub- 
stances containing  nitrogen. 

Ammonia  is  prepared  from  an  ammonium  salt  by  treat 
ing  it  with  a  strong  base.     Ammonium  chloride  and  lime 
are  commonly  used. 

With  acids  ammonia  forms  salts  which  are  known  as 
ammonium  salts,  and  in  which  the  group  NH4  is  believed 
to  play  the  part  of  a  metal.  This  hypothetical  metal  is 
called  ammonium. 

Ammonia  consists  of  14  parts  by  weight  of  nitrogen  to  3  of 
hydrogen.  The  gases  are  combined  in  the  proportion  of 
1  volume  of  nitrogen  to  3  volumes  of  hydrogen.  The 
4  volumes  thus  combined  condense  to  2  volumes  of 
ammonia. 


1 66  INTRODUCTION    TO   CHEMISTRY. 

There  is  always  a  simple  relation  between  the  volumes 
of  combining  gases  and  the  volume  of  the  compound 
formed  if  it  is  a  gas. 

A  comparison  of  the  specific  gravities  of  the  gaseous 
elements  shows  that  these  bear  to  one  another  the  same 
relation  as  the  atomic  weights. 

Nitric  acid  is  prepared  from  a  nitrate  by  treating  it  with 
sulphuric  acid.  It  is  comparatively  unstable,  giving  up 
oxygen  easily.  With  metals  it  yields  salts,  but  the  action 
involves  the  reduction  of  a  part  of  the  acid,  and  leads  to 
the  formation  of  various  products,  among  which  may  be 
nitrous  oxide,  N20;  nitric  oxide,  NO;  nitrous  anhydride, 
N203;  and  nitrogen  peroxide,  N02.  Under  some  circum- 
stances, the  action  may  even  go  far  enough  to  form 
ammonia.  Nitrous  acid  itself  is  unstable,  breaking  up 
into  the  anhydride,  N203 ,  and  water. 

Anhydrides  are  substances  which,  when  brought  together 
with  water,  combine  with  it  to  form  acids. 

Though  nitrous  oxide  is  formed  by  reduction  of  nitric 
acid,  it  is  best  prepared  in  pure  condition  by  heating 
ammonium  nitrate.  It  supports  combustion  well. 

Nitric  oxide  is  made  by  reduction  of  nitric  acid  by 
means  of  copper.  It  combines  directly  with  oxygen, 
forming  the  strongly-colored  and  disagreeable-smelling 
nitrogen  peroxide. 

Nitrogen  peroxide  gives  up  a  part  of  its  oxygen  easily, 
and  is  hence  a  good  oxidizing  agent.  It  is  thus  reduced 
to  nitric  oxide,  which  in  the  air  takes  up  oxygen. 


CHAPTER  XL 
CARBON. 

Carbon  in  Plants  and  Animals. — Most  substances  of 
vegetable  or  animal  origin  blacken  when  they  are  heated 
to  a  sufficiently  high  temperature,  and  if  heated  in  the  air 
they  burn  up,  as  we  say.  This  is  due  to  the  fact  that 
nearly  all  animal  and  vegetable  substances  contain  the 
element  carbon.  When  they  are  heated  the  other  elements 
present  are  first  driven  off  in  various  forms  of  combina- 
tion, while  the  carbon  is  the  last  to  go.  If  the  heating  is 
carried  on  in  the  air,  the  carbon  finally  combines  with 
oxygen  to  form  a  colorless  gas — it  burns  up.  Carbon 
is  the  central  element  of  organic  nature.  All  living 
things  contain  this  element  as  an  essential  constituent. 
The  number  of  the  compounds  which  it  forms  is 
almost  infinite,  and  they  present  such  peculiarities 
that  they  are  commonly  treated  under  a  separate 
head,  "Organic  Chemistry,"  There  is  no  good  reason 
for  this,  except  the  large  number  of  the  compounds. 
For  the  present  it  will  suffice  to  study  the  chemistry  of 
the  element  itself,  and  of  a  few  of  its  simpler  compounds, 
and  farther  on  a  few  chapters  devoted  to  some  of  its  most 
important  compounds  will  be  presented. 

Occurrence, — From  what  has  already  been  said,  it  will 
be  seen  that  carbon  occurs  in  nature  for  the  most  part  in 
combination  with  other  elements.  It  occurs  not  only  in 

167 


i68  INTRODUCTION    TO   CHEMISTRY. 

living  things,  but  in  their  fossil  remains,  as  in  coal. 
Coal-oil,  or  petroleum,  consists  of  a  large  number  of  com- 
pounds which  contain  only  carbon  and  hydrogen.  Most 
products  of  plant-life  contain  the  elements  carbon, 
hydrogen,  and  oxygen.  Among  the  more  common  of 
these  may  be  mentioned  sugar,  starch,  cellulose,  etc. 
Most  products  of  animal  life  contain  carbon,  hydrogen, 
oxygen,  and  nitrogen.  Among  them  may  be  mentioned 
albumin,  fibrin,  casein,  urea,  etc.  Carbon  occurs  in  the 
atmosphere  in  the  form  of  carbon  dioxide.  [What  evi- 
dence have  we  already  had  of  the  presence  of  carbon 
dioxide  in  the  air  ?]  It  also  occurs  in  the  form  of  salts  of 
carbonic  acid — the  carbonates,  which  are  widely  dis- 
tributed, forming  whole  mountain-ranges.  Limestone, 
marble,  and  chalk  are  calcium  carbonate. 

Uncombined,  the  element  occurs  pure  in  two  very 
different  forms  in  nature:  (1)  as  diamond;  and  (2)  as 
graphite,  or  plumbago. 

Before  presenting  the  evidence  that  leads  to  the  conclu- 
sion that  diamond  and  graphite  are  only  modifications  of 
the  same  element,  and  that  while  closely  related,  to  each 
other  they  are  also  equally  closely  related  to  charcoal,  it 
will  be  best  to  study  separately  the  properties  of  each  of 
these  three  substances. 

1.  Diamond. — The  diamond  is  found  in  but  few  places 
on  the  earth.  Little  is  known  as  to  the  conditions 
which  gave  rise  to  its  formation.  The  celebrated 
diamond-beds  are  in  India,  Borneo,  Brazil,  and  South 
Africa.  When  found,  diamonds  are  covered  with  an 
opaque  layer,  which  must  be  removed  before  the  beautiful 
properties  appear.  The  crystals  are  sometimes  what  are 
known  as  octahedrons;  that  is  to  say,  they  are  regular 
eight-sided  figures,  though  usually  they  are  somewhat 
more  complicated.  It  is  the  hardest  substance  known. 


GRAPHITE -AMORPHOUS   CARBON.  169 

If  heated  to  a  very  high  temperature  without  access  of 
air,  it  swells  up  and  is  converted  into  a  black  mass  resem- 
bling graphite.  This  change  takes  place  without  loss  in 
weight.  Heated  to  a  high  temperature  in  oxygen,  it 
burns  up,  yielding  only  carbon  dioxide.  It  is  insoluble  in 
all  ordinary  liquids. 

Moissan  has  made  small  diamonds  by  dissolving'  char- 
coal in  molten  iron  in  a  crucible  in  an  electric  furnace, 
and  then  plunging  the  crucible  into  water.  In  this  case 
the  outside  of  the  solution  is  quickly  solidified  while  the 
inner  portions  are  still  liquid  and  under  strong  pressure. 
Under  these  circumstances  the  carbon  is  deposited  from 
the  solution  in  small  crystals  that  have  the  properties  of 
diamonds. 

2.  Graphite, — Graphite,  or  plumbago,  is  found  in  nature 
in  large  quantities.     Sometimes  it  is  crystallized,  but  in 
forms    entirely    different    from    those    assumed    by   the 
diamond.     It  can  be  prepared  artificially  by   dissolving 
charcoal  in  molten  iron,  from  which  solution  graphite  is 
deposited  on  cooling.     It  has  a  grayish-black  color  and  a 
metallic   lustre.     It   is   quite  soft,  leaving  a  leaden-gray 
mark  on  paper  when  drawn  across  it,  and  is  hence  used  in 
the  manufacture  of  so-called  lead  pencils.     It  is  sometimes 
called  black-lead. 

When  heated  without  access  of  air  it  remains  unchanged. 
Heated  to  a  very  high  temperature  in  the  air,  or  in  oxygen, 
it  burns  up,  forming  only  carbon  dioxide.  Like  the 
diamond,  it  is  insoluble  in  all  ordinary  liquids. 

3.  Amorphous   Carbon. — All  forms  of   carbon  that  are 
not  diamond   or  graphite  are  included  under  the  name 
amorphous  carbon.     The  name  signifies  simply  that  it  is 
not  crystallized.     The  most  common  form  of  amorphous 
carbon  is  ordinary  charcoal. 


170  INTRODUCTION   TO   CHEMISTRY. 

Charcoal  is  that  form  of  carbon  which  is  made  by  the 
ehat 'ring  process,  which  consists  simply  in  heating  without 
a  free  supply  of  air.  The  substance  almost  exclusively  used 
in  the  manufacture  of  charcoal  is  wood.  As  has  already 
been  stated,  wood  is  made  of  a  large  number  of  substances, 
nearly  all  of  which,  however,  consist  of  the  three  elements 
carbon,  hydrogen,  and  oxygen.  One  of  the  chief  constit- 
uents of  all  kinds  of  wood  is  cellulose.  Now,  when  a  piece 
of  wood  is  heated  to  the  kindling  temperature  in  the 
air,  it  burns.  The  chemical  changes  that  take  place 
are  complex  under  ordinary  circumstances;  but  if  care  is 
taken,  the  combustion  can  be  made  complete,  when  all  the 
carbon  is  converted  into  carbon  dioxide,  and  all  the 
hydrogen  into  water.  If,  on  the  other  hand,  the  air  is 
prevented  from  coming  in  contact  with  the  wood  in  suffi- 
cient quantity  to  effect  complete  combustion,  the  hydrogen 
is  given  off  partly  as  water  and  partly  in  the  form  of 
volatile  compounds  containing  carbon  and  oxygen.  Most 
of  the  carbon,  however,  is  left  behind  as  charcoal,  as  there 
is  not  enough  oxygen  to  convert  it  into  carbon  dioxide. 

A  Charcoal-kiln. — A  charcoal-kiln  consists  essentially 
of  a  pile  of  wood  so  arranged  as  to  leave  spaces  between 
the  pieces.  The  pile  is  covered  with  a  structure  of  brick- 
work or  with  some  rough  material  through  which  the  air 
will  not  pass  easily,  as,  for  example,  a  mixture  of  powdered 
charcoal,  turf,  and  earth.  Openings  are  left  in  this  cover- 
ing so  that  after  it  is  kindled  the  wood  wrill  continue  to 
burn  slowly.  The  changes  above  mentioned  take  place, 
the  gases  or  volatile  substances  passing  out  at  the  top  of 
the  kiln,  and  appearing  as  a  thick  smoke.  In  due  time 
the  holes  through  which  the  air  gains  access  to  the  wood, 
and  which  also  make  the  burning  possible,  are  closed,  and 
the  burning  stops.  Charcoal,  which  is  impure  amorphous 
carbon,  is  left  behind.  As  wood  always  contains  some  in- 


WOOD-CHARCOAL— COKE.  -LAMP  BLACK.  171 

combustible  substances  in  small  quantity,  these  are,  of 
course,  found  in  the  charcoal.  When  the  wood  or  char- 
coal is  burned,  these  substances  remain  behind  as  the  ash. 

Wood-charcoal. — Ordinary  charcoal  is  a  black,  compara- 
tively soft  substance.  It  burns  in  the  air,  though  not 
easily  unless  the  gases  formed  are  constantly  removed  and 
fresh  air  is  supplied,  as  when  the  draught  is  good  or  a  pair 
of  bellows  is  used.  It  burns  readily  in  oxygen  (see  Experi- 
ment 22).  The  product  of  the  combustion  in  oxygen  and 
in  air,  when  the  conditions  are  favorable,  is  carbon  dioxide, 
C02.  In  the  air,  when  the  draught  is  bad,  another  com- 
pound of  carbon  and  oxygen,  carbon  monoxide,  CO,  is 
formed.  Heated  without  access  of  air,  charcoal  remains 
unchanged.  Charcoal  is  insoluble  in  all  ordinary  liquids. 

Coke. — Besides  wood-charcoal,  there  are  other  forms  of 
amorphous  carbon,  which  are  manufactured  for  special  pur- 
poses, or  are  formed  in  processes  carried  on  for  the  sake 
of  other  products.  Coke  is  a  form  of  amorphous  carbon 
which  is  made  by  heating  ordinary  gas-coal  without  access 
of  air,  as  is  done  on  a  large  scale  in  the  manufacture  of 
coal-gas.  Coke  bears  to  coal  about  the  same  relation  that 
charcoal  bears  to  wood. 

Lamp-black  is  a  very  finely  divided  form  of  charcoal 
which  is  deposited  on  cold  objects  placed  in  the  flames  of 
burning  oils.  The  oils  consist  almost  exclusively  of  carbon 
and  hydrogen.  When  burned  in  the  air  they  yield  carbon 
dioxide  and  water.  If  the  flame  is  cooled  down  by  any 
means,  or  if  the  supply  of  air  is  partly  cut  off,  the  carbon 
is  not  completely  burned;  the  flame  "smokes,"  and 
deposits  soot.  This  soot  is  largely  made  up  of  fine  particles 
of  carbon.  It  is  used  in  the  manufacture  of  printer's  ink. 
Carbon  is  acted  upon  directly  by  very  few  substances,  and 
is  not  soluble,  so  that  it  is  impossible  to  destroy  the  color 


i?2  INTRODUCTION   TO   CHEMISTRY. 

of  printer's  ink  without   destroying   the   material  upon 
which  it  is  impressed. 

Bone-black,  or  Animal  Charcoal,  is  a  form  of  amorphous 
carbon  which  is  made  by  charring  bones.  Unless  treated 
with  an  acid  it  contains  the  incombustible  substances  con- 
tained in  bone,  as  calcium  phosphate,  etc. 

Charcoal  Filters. — Bone-black  and  wood-charcoal  are 
very  porous  and  have  the  power  to  absorb  gases.  When 
placed  in  air  containing  offensive  gases,  these  are  ab- 
sorbed and  the  air  is  thus  purified.  When  water  contain- 
ing disagreeable  substances  is  treated  with  charcoal,  these 
are  wholly  or  partly  absorbed  and  the  water  improved. 
Charcoal  niters  are  therefore  extensively  used.  A  charcoal 
filter  to  be  efficient  should  be  of  good  size,  and  from  time 
to  time  the  charcoal  should  be  renewed.  The  small  filters 
which  are  screwed  into  faucets  are  of  little  value,  as  the 
charcoal  soon  becomes  charged  with  the  objectionable 
material  of  the  water. 

Some  coloring  matters  can  be  removed  from  liquids  by 
passing  the  latter  through  bone-black  filters.  On  the  large 
scale,  this  fact  is  taken  advantage  of  in  the  refining  of 
sugar.  The  solution  of  sugar  first  obtained  from  the  cane 
or  beet  is  highly  colored;  and  if  it  were  evaporated,  the 
sugar  deposited  from  it  would  be  dark-colored.  If,  how- 
ever, the  solution  is  first  passed  through  bone-black  filters, 
the  color  is  removed,  and  now,  on  evaporating,  white 
sugar  is  deposited.  In  the  laboratory  constant  use  is  made 
of  this  method  for  the  purpose  of  purifying  liquids. 

EXPERIMENT  86. — Make  a  filter  of  bone-black  by  fitting  a  paper 
filter  into  a  funnel  12  to  15  cm.  (5  to  6  inches)  in  diameter  at  its 
mouth.  Half-fill  this  with  bone-black.  Make  a  dilute  solution 
of  indigo.  Pour  it  through  the  filter.  If  the  conditions  are  right 
the  solution  will  pass  through  colorless. — Do  the  same  thing  with 
a  dilute  solution  of  ink. — If  the  color  is  not  completely  re- 


COAL.  173 

moved  by  one  filtering,  filter  it  again. — The  color  can  also  be 
removed  from  solutions  by  putting  some  bone-black  into  them 
and  boiling  for  a  time. — Try  this  with  half  a  litre  each  of  the 
ink  and  indigo  solutions  used  in  the  first  part  of  the  experi- 
ment. Use  about  4  to  5  grams  bone-black  in  each  case.  Shake 
the  solution  frequently  while  heating. 

Wood  is  Charred  to  Preserve  it, — Charcoal  does  not 
suffer  decay  in  the  air  or  under  water  nearly  as  readily  as 
wood.  This  is  another  way  of  stating  the  chemical  fact 
that  the  substances  of  which  wood  is  made  up  are  more 
susceptible  to  the  action  of  other  chemical  substances  than 
charcoal  is.  The  relative  ease  with  which  charcoal  and 
wood  burn  in  the  air  illustrates  this  fact.  Piles  driven 
below  the  surface  of  water  are  charred  to  protect  them  from 
the  action  of  those  substances  which  cause  decay.  Most 
of  the  houses  in  Venice  stand  on  piles  of  wood  which  have 
been  charred.  Oak  stakes  have  quite  recently  been  found 
in  the  Thames  where,  according  to  Tacitus,  the  Britons 
fixed  stakes  to  prevent  the  passage  of  Caesar  and  his  army. 

Coal. — Under  this  head  are  included  a  great  many  kinds 
of  impure  amorphous  carbon  which  occur  ready-formed  in 
nature.  Although  an  almost  infinite  number  of  kinds  of 
coal  are  found,  for  ordinary  purposes  they  are  classified  as 
hard  and  soft  coals,  or  anthracite  and  bituminous  coals. 
Then  there  are  substances  more  nearly  allied  to  wood  called 
lignite,  and  those  which  represent  a  very  early  stage  in  the 
process  of  coal-formation,  as,  for  example,  peat. 

A  close  examination  of  all  of  these  varieties  has  shown 
that  they  have  been  formed  by  the  gradual  decomposition 
of  vegetable  material  in  an  insufficient  supply  of  air.  The 
process  has  been  going  on  for  ages.  Sometimes  the  sub- 
stances have,  at  the  same  time,  been  subjected  to  great 
pressure,  as  can  be  seen  from  the  position  in  which  they 
occur  in  the  earth.  The  products  in  the  earlier  stages  of 


174  INTRODUCTION   TO  CHEMISTRY. 

the  coal -form  ing  process  are,  naturally,  more  closely  allied 
to  wood  than  those  in  the  later  stages. 

.All  forms  of  coal  contain  other  substances  in  addition  to 
the  carbon.  The  soft  coals  are  particularly  rich  in  other 
substances.  When  heated  they  give  off  a  mixture  of  gases 
and  the  vapors  of  volatile  liquids.  The  gases  are,  for  the 
most  part,  useful  for  illuminating  purposes.  The  liquids 
form  a  black;  tarry  mass  known  as  coal-tar,  from  which  are 
obtained  many  valuable  compounds  of  carbon.  The  gases 
are  passed  through  water  for  the  purpose  of  removing 
certain  impurities.  This  water  absorbs  ammonia  and 
forms  the  ammonia-water  of  the  gas-works,  which,  as  has 
been  stated,  is  the  principal  source  of  ammonia. 

Diamond,  Graphite,  and  Charcoal  are  Different  Forms  of 
the  Element  Carbon. — An  element  is  a  kind  of  matter  from 
which  no  simpler  kind  of  matter  can  be  obtained  by  any 
means  now  known  to  chemists.  From  hydrogen  nothing 
but  hydrogen  can  be  obtained,  except  by  bringing  it 
together  with  some  other  element;  from  nitrogen,  nothing 
but  nitrogen,  etc.  In  the  case  of  carbon,  however,  the 
element  appears  in  three  forms  which  differ  markedly  from 
one  another.  It  is  difficult  to  conceive  that  the  soft,  black 
charcoal  and  the  dull,  gray,  soft  graphite  are  chemically 
identical  with  the  hard,  transparent,  brilliant  diamond. 
Yet  this  is  undoubtedly  the  case,  as  can  be  proved  by  a 
very  simple  experiment.  Each  of  the  substances  when 
burned  in  oxygen  yields  carbon  dioxide.  Now,  the  com- 
position of  carbon  dioxide  is  known,  so  that  if  the  weight 
of  carbon  dioxide  formed  in  a  given  experiment  is  known, 
the  weight  of  carbon  contained  in  it  is  also  known.  When 
a  gram  of  pure  charcoal  is  burned  it  yields  3|  grams  of 
carbon  dioxide,  and  in  this  quantity  of  carbon  dioxide 
there  is  contained  exactly  1  gram  of  carbon.  Further, 
when  a  gram  of  graphite  is  burned  the  same  weight 


DIFFERENT  FORMS  OF  SAME  SUBSTANCE.          i?5 

(3f  grams)  of  carbon  dioxide  is  formed  as  in  the  case  of 
charcoal;  and  the  same  is  true  of  diamond.  It  follows 
from  these  facts  that  the  three  forms  of  matter  known  as 
charcoal,  graphite,  and  diamond  consist  only  of  the 
element  carbon. 

[PROBLEM. — How  much  carbon  dioxide,  COa ,  should  be  ob- 
tained by  burning  0.5  gram  diamond?  The  atomic  weight  of 
carbon  is  12.] 

Other  Examples  of  the  Occurrence  of  a  Substance  in 
Different  Forms. — That  one  and  the  same  substance  can 
appear  in  markedly  different  forms  under  different  condi- 
tions is  seen  in  the  case  of  water.  Hail  and  snow  would 
hardly  be  suspected  of  being  the  same  substance  by  one 
who  was  not  quite  familiar  with  them.  The  difference  in 
this  case,  as  in  that  under  discussion,  is  believed  to  be  due 
to  the  way  in  which  the  small  particles  of  which  the  sub- 
stances are  made  up  are  arranged  with  reference  to  one 
another.  If  we  had  a  number  of  small  pieces  of  wood  all 
of  the  same  size  and  shape,  say  cubical,  and  should  care- 
fully arrange  these  in  some  regular  way,  we  might  easily 
make  a  comparatively  compact  mass  of  them,  and  the  mass 
would  have  a  regular  form.  We  might  arrange  them, 
further,  in  a  second  way  with  regularity.  And  we  might 
simply  throw  the  pieces  together  in  a  jumble.  These  three 
kinds  of  arrangement  would  represent,  in  a  rough  way,  fhe 
difference  between  the  three  forms  of  carbon.  Each  pile 
would  be  made  of  wood,  but  still  in  outward  appearance 
they  would  differ  from  one  another. 

Common   Properties  of  the  Three  Forms  of  Carbon. — 

Notwithstanding  the  marked  differences  in  their  appear- 
ance, the  three  forms  of  carbon  have,  as  we  have  seen, 
some  properties  in  common.  They  are  insoluble  in  all 
ordinary  liquids.  They  are  tasteless  and  inodorous.  They 


I?6  INTRODUCTION   TO  CHEMISTRY. 

are    infusible.     When    heated  without  access  of  air,  they 
remain  unchanged,  unless  the  temperature  is  very  high. 

Chemical  Conduct  of  Carbon. — At  ordinary  temperatures 
carbon  is  an  inactive  element.  If  it  is  left  in  contact  with 
any  one  of  the  elements  thus  far  studied, — viz.,  hydrogen, 
oxygen,  chlorine,  and  nitrogen,— no  change  takes  place. 
Indeed,  unless  the  temperature  is  raised  it  will  not  com- 
bine with  any  other  element.  At  higher  temperatures, 
however,  it  combines  with  other  elements,  especially  with 
oxygen,  with  great  ease.  Under  some  conditions  it 
combines  also  with  nitrogen,  with  hydrogen,  and  with 
many  other  elements.  It  combines  with  oxygen  either 
directly,  as  when  it  burns  in  the  air  or  in  oxygen;  or  it 
abstracts  oxygen  from  some  of  the  oxides. 

Direct  Union  of  Carbon  and  Oxygen. — This  has  already 
been  illustrated  in  Experiment  #2,  and  is  also  illustrated 
in  every  charcoal-furnace.  That  carbon  dioxide  is  the 
product  may  be  shown  by  passing  the  gas  into  lime-water 
or  baryta-water,  when  insoluble  calcium,  or  barium,  car- 
bonate will  be  thrown  down. 

EXPERIMENT  87. — Put  a  small  piece  of  charcoal  in  a  hard-glass 
tube.  Pass  oxygen  through  the  tube,  at  the  same  time  heating 
it.  Pass  the  gases  into  clear  lime-water.  Arrange  the  appa- 
ratus as  shown  in  Fig.  40. 

A  is  a  large  bottle  containing  oxygen  ;  B  is  a  cylinder  contain- 
ing sulphuric  acid  ;  C  is  a  U  tube  containing  calcium  chloride  ; 
D  is  the  hard-glass  tube  containing  the  charcoal;  E  is  the  cylin- 
der with  clear  lime-water.  In  what  previous  experiment  was 
this  method  of  showing  the  formation  of  carbon  dioxide  used  ? 
The  reason  why  it  is  used  is  simply  that  an  insoluble  compound 
is  formed,  and  this  can  be  seen,  and  it  can  be  separated  from  the 
liquid  and  examined.  The  reaction  is  represented  thus  : 

Ca(OH)a      +      C0a  OaCOs      +      HaO. 

Lime.  Carbon  dioxide.  Calcium  carbonate. 


ABSTRACTION   OF  OXYGEN  FROM   COMPOUNDS.      17? 


No  other  common  gas  acts  in  this  way  on  lime-water.     Hence, 
when,  under  ordinary  circumstances,  a  gas  is  passed  into  lime- 


FIG.  40. 

water  and  an  insoluble  substance  is  formed,  we  may  conclude 
that  the  gas  is  carbon  dioxide. 

Abstraction  of  Oxygen   from   Compounds  by  Means  of 
Carbon, — This  can  be  illustrated  in  a  number  of  ways. 

EXPERIMENT  88. — Mix  together  2  or  3  grams  powdered  copper 
oxide,  CuO,  and  an  equal  bulk  of  pow- 
dered charcoal  ;    heat    in   a   hard-glass 
tube  to  which  is  fitted  an  outlet-tube,  as 
shown  in  Fig.  41. 

Pass  the  gas  which  is  given  off  into 
lime-water  contained  in  a  test-tube.  Is 
it  carbon  dioxide  ?  What  evidence  have 
you  that  oxygen  has  been  extracted  from 
the  copper  oxide  ?  What  is  the  appear- 
ance of  the  substance  left  in  the  tube  ? 
Does  it  suggest  the  metal  copper  ?  Treat  FIG.  41. 

a  little  of  it  with  strong  nitric  acid.     What  should  take  place  if 
the  substance  is  metallic  copper?    (See  Experiment  78.)     What 


I?8  INTRODUCTION    TO   CHEMISTRY. 

does  take  place  ?    The  reaction  between  the  charcoal  and  the 
copper  oxide  is  represented  thus: 

2CuO  +  C  —  2Cu  +  CO2. 

EXPERIMENT  89.— Perform  a  similar  experiment  with  a  little 
white  arsenic  in  a  small  glass  tube  closed  at  one  end.  Take 
about  equal  parts  of  charcoal  and  arsenic.  White  arsenic  is  a 
compound  of  the  element  arsenic  and  oxygen,  of  the  composition 
represented  by  the  formula  As3O3.  The  reaction  that  takes  place 
when  it  is  heated  with  charcoal  is  represented  thus  : 

2AsaO3  -f  30  =  4As  +  3CO,. 

The  element  arsenic  is  volatile,  and  is  hence  driven  upward 
and  deposited  on  the  inside  of  the  tube  above  the  mixture,  in  the 
form  of  a  mirror  with  metallic  lustre. 

Keduction. — The  abstraction  of  oxygen  from  a  com- 
pound is  known  as  reduction,  as  has  already  been  explained. 
Hence  carbon  is  called  a  reducing  agent.  It  is  indeed  the 
reducing  agent  that  is  most  extensively  used  in  the  arts. 
Its  chief  use  is  in  extracting  metals  from  their  ores. 
Thus,  iron  does  not  occur  in  nature  as  iron,  but  in  com- 
bination with  other  elements,  especially  with  oxygen.  In 
order  to  get  the  metal,  the  ore  must  be  reduced,  or,  in 
other  words,  the  oxygen  must  be  extracted.  This  is 
accomplished  by  heating  it  with  some  form  of  carbon, 
either  charcoal  or  coke. 

[What  other  element  already  studied  acts  as  a  reducing 
agent  ?  Give  an  example  of  its  reducing  power.] 


CHAPTER   XII. 
SOME   OF  THE   SIMPLER   COMPOUNDS   OF  CARBON. 

Compounds  of  Carbon  with  Hydrogen, — Carbon  com- 
bines with  hydrogen  in  a  great  many  different  proportions, 
the  compounds  being  known  as  hydrocarbons.  Among 
the  simpler  examples  are  marsh-gas,  or  fire-damp,  CH4; 
ethylene,  C2H4;  acetylene,  C2H2;  and  benzene,  C6H6.  These 
together  with  a  few  others  will  be  taken  up  in  a  later 
chapter. 

Carbon  Dioxide,  C02. — The  principal  compound  of  car 
bon  and  oxygen  is  carbon  dioxide,  COB,  commonly  called 
carbonic-acid  gas.  Under  the  head  of  The  Atmosphere 
attention  was  called  to  the  fact  that  this  gas  is  a  constant 
constituent  of  the  air,  though  it  is  present  in  relatively 
small  quantity.  It  issues  from  the  earth  in  many  places, 
particularly  in  the  neighborhood  of  volcanoes.  Many 
mineral  waters  contain  it  in  large  quantity,  as  the  waters 
of  Pyrmont,  Selters,  and  the  Geyser  Spring  at  Saratoga. 
In  small  quantity  it  is  present  in  all  natural  waters.  In 
combination  with  bases  it  occurs  in  enormous  quantities, 
particularly  in  the  form  of  calcium  carbonate,  CaC03 , 
varieties  of  which  are  ordinary  limestone,  chalk,  marble, 
and  calc-spar.  Dolomite,  a  compound  consisting  of  calcium 
carbonate  and  magnesium  carbonate,  MgC03,  enters 
largely  into  the  structure  of  some  mountain -ranges,  as,  for 
example,  the  Swiss  Alps. 

Carbon  Dioxide  given  off  from  the  Lungs. — Carbon 
dioxide  is  constantly  formed  in  many  natural  processes. 


i8o 


INTRODUCTION    TO   CHEMISTRY. 


Thus,  all  animals  that  breathe  in  the  air  give  off  carbon 
dioxide  from  their  lungs. 

EXPERIMENT  90.— Force  the  gases  from  the  lungs  through  some 
lime-water  by  means  of  an  apparatus  arranged  as  shown  in  Fig. 
42.  What  is  formed  ?  Add  a  few  drops  of  hydrochloric  acid. 
What  takes  place  ? 

Carbon  Dioxide  formed  in  Com- 
bustion, in  Decay,  and  in  Fer- 
mentation.— That  carbon  dioxide 
is  formed  in  the  combustion  of 
charcoal  and  wood  has  already 
been  shown.  In  a  similar  way  it 
can  be  shown  that  the  gas  is 
formed  whenever  any  of  our 
ordinary  combustible  materials 
are  burned.  From  our  fires,  as 
from  our  lungs,  and  from  the 
FIG.  42.  lungs  of  all  animals,  then,  carbon 

dioxide  is  constantly  given   off. 

Further,  the  natural  processes  of  decay  of  both  vegetable 
and  animal  matter  tend  to  convert  the  carbon  of  this 
matter  into  carbon  dioxide,  which  is  then  spread  through 
the  air.  The  process  of  alcoholic  fermentation,  and  some 
other  similar  processes,  also  give  rise  to  the  formation  of 
carbon  dioxide.  In  all  fruit- juices  sugar  is  contained. 
When  the  fruits  ripen,  fall  off,  and  lie  exposed  to  the  air, 
fermentation  takes  place,  and  the  sugar  is  changed  to 
alcohol  and  carbon  dioxide. 

It  is  clear,  therefore,  that  there  are  many  important 
sources  of  supply  of  carbon  dioxide,  and  it  will  readily  be 
understood  why  the  gas  should  be  found  everywhere  in  the 
air. 

Decomposition  of  Carbonates  by  Acids. — The  easiest  way 
to  get  carbon  dioxide  unmixed  with  other  substances  is  to 


DECOMPOSITION   OF  CARBONATES  181 

add  an  acid  to  a  carbonate.     Whenever  an  acid  is  added 
to  a  carbonate  there  is  an  evolution  of  gas. 

EXPERIMENT  91.  —  In  test-tubes  add  successively  dilute  hydro- 
chloric, sulphuric,  nitric,  and  acetic  acids  to  a  little  sodium  car- 
bonate. In  each  case  pass  the  gas  given  off  through  lime-water  ; 
and  insert  a  burning  stick  in  the  upper  part  of  each  tube.  —  Per- 
form the  same  experiment  with  small  pieces  of  marble. 

Comparison  of  this  Decomposition  with  other  similar 
Acts.  —  The  decomposition  of  the  salts  of  carbonic  acid  by 
other  acids  affords  another  illustration  of  the  principle 
that  is  involved  in  setting  nitric  acid  free  from  a  nitrate,  or 
hydrochloric  acid  from  a  chloride,  by  means  of  sulphuric 
acid.  The  non-volatile  acid  drives  out  the  volatile  acid. 
When,  for  example,  hydrochloric  acid  is  added  to  sodium 
carbonate  the  first  action  consists  in  an  exchange  of  the 
hydrogen  of  the  acid  for  the  metal  of  the  carbonate  : 


Na2COs  +  2HC1  =  2NaCl  +  H2COS. 

If  sulphuric  acid  is  used,  the  reaction  is  represented  thus  : 
Na2C08  +  11,80,=  Na$04  +  H2CO,. 


This  reaction  is  analogous  to  that  which  takes  place 
between  sodium  nitrate  and  sulphuric  acid  in  the  prepara- 
tion of  nitric  acid  : 

SNaNO,  +  H2S04  =  Na2S04  +  2HNO,. 

Carbonic  acid,  however,  is  an  unstable  substance,  and 
breaks  down  into  water  and  carbon  dioxide  as  soon  as  it  is 
liberated  from  its  salts  : 


H2C03  =  H20  +  C0 


As  carbon  dioxide  is  a  gas  it  escapes. 

It  will  be  seen  that  the  decomposition  of  carbonic  acid 
into  carbon  dioxide  and  water  is  analogous  to  the  decom- 


INTRODUCTION   TO  CHEMISTRY. 


position  of  nitrous  acid,  HN02  ,  into  nitrogen  trioxide  and 
water;  and  similar  to  the  decomposition  of  ammonium 
hydroxide  into  ammonia  and  water. 

[What  is  a  compound  called  which  bears  to  an  acid  the 
relation  that  carbon  dioxide  bears  to  carbonic  acid  ?] 

Preparation  of  Carbon  Dioxide.  —  For  the  purpose  of 
preparing  carbon  dioxide  in  the  laboratory,  calcium  car- 
bonate in  the  form  of  marble,  or  limestone,  and  hydro- 
chloric acid  are  commonly  used.  The  reaction  involved  is 
represented  thus: 


CaC03  +  2HC1  =  CaCl2 


C02  +  H2O. 


EXPERIMENT  92.  —  Arrange  an  apparatus  as  shown  in  Fig.  43. 
In  the  flask  put  some  pieces  of  marble  or 
limestone,  and  pour  ordinary  hydrochloric 
acid  on  it.  The  gas  should  be  collected  by 
displacement  of  air,  the  vessel  being  placed 
with  the  mouth  upward,  as  the  gas  is  much 
heavier  than  air.  Collect  several  cylinders 
or  bottles  full  of  the  gas.  Into  one  introduce 
successively  a  lighted  candle,  a  burning  stick, 
a  bit  of  burning  phosphorus  in  a  deflagrating- 
spoon.  What  takes  f)lace  ?  With  another 
proceed  as  if  pouring  water  from  it.  Pour 
the  invisible  gas  upon  the  flame  of  a  burning 
candle.  Pour  some  of  the  gas  from  one  ves- 
sel to  another,  and  show  that  it  has  been 
transferred.  Weigh  a  beaker  on  a  balance, 
and  pour  carbon  dioxide  into  it.  Give  an 
account  of  the  results  obtained  and  state  the 
conclusions  you  are  justified  in  drawing  from 
FIG.  43.  what  you  have  seen. 

Physical  Properties  of  Carbon  Dioxide.  —  Carbon  dioxide 
is  a  colorless  gas.  When  subjected  to  a  low  temperature 
and  high  pressure  it  is  converted  into  a  liquid;  and  when 
some  of  the  liquid  is  exposed  to  the  air,  evaporation  takes 
place  so  rapidly  that  a  great  deal  of  heat  is  absorbed,  and 


CHEMICAL  PROPERTIES   OF  CARBON  DIOXIDE.       183 

some  of  the  liquid  becomes  solid.     The  gas  has  a  slightly 
acid  taste  and  smell. 

Carbon  dioxide  is  much  heavier  than  air,  its  specific 
gravity  being  1.529.  A  litre  of  the  gas  under  standard 
conditions  of  temperature  and  pressure  weighs  1.971 
grams.  It  dissolves  in  water,  one  volume  of  water  dis- 
solving about  one  volume  of  the  gas  at  the  ordinary  tem- 
perature. As  is  the  case  with  all  gases,  when  the  pressure 
is  increased  the  water  dissolves  more  gas ;  and  when  the 
pressure  is  removed  the  gas  escapes  again.  The  so-called 
"  soda-water  "  is  simply  water  charged  with  carbon  dioxide 
under  pressure.  The  escape  of  the  gas,  when  the  water  is 
drawn,  is  familiar  to  every  one.  The  carbon  dioxide  used 
in  charging  the  water  is  generally  made  from  a  sodium 
salt  of  carbonic  acid  known  as  "  bicarbonate  of  soda." 

Chemical  Properties  of  Carbon  Dioxide. — Carbon  dioxide 
is  not  combustible,  nor  does  it  support  combustion.  It 
is  not  combustible  for  the  same  reason  that  water  is  not; 
because  it  already  holds  in  combination  all  the  oxygen  it 
has  the  power  to  combine  with.  Before  it  can  burn  again, 
it  must  first  be  decomposed.  Carbon  has  the  power  to 
combine  with  oxygen,  and  in  so  doing  it  gives  rise  to  the 
formation  of  a  definite  quantity  of  heat.  A  kilogram  of 
carbon  represents  a  definite  quantity  of  energy,  which  we 
can  get  first  in  the  form  of  heat  and  then  convert  into 
other  forms,  as  electricity,  motion,  etc.  After  the  kilo- 
gram of  carbon  has  been  burned,  it  no  longer  represents 
the  energy  it  did  in  the  form  of  carbon.  A  body  of  water 
elevated  ten  or  fifteen  feet  represents  a  definite  quantity 
of  energy  which  can  be  obtained  by  allowing  the  water  to 
fall  upon  the  paddles  of  a  water-wheel  connected  with  the 
machinery  of  a  mill.  After  the  water  has  fallen,  however, 
it  no  longer  has  power  to  do  work,  or  it  has  no  energy. 
In  order  that  it  may  again  do  work,  it  must  again  be  lifted. 


1 84  INTRODUCTION   TO  CHEMISTRY. 

Not  only  does  carbon  dioxide  not  burn,  but  it  does  not 
support  combustion.  Although  it  contains  a  large  quan- 
tity of  oxygen  in  combination,  it  does  not  as  a  rule  give  it 
up  to  other  substances. 

[What   gas   containing    oxygen    in    combination   with 
another  element  does  support  combustion  ?] 

Respiration. — It  was  stated  above  that  carbon  dioxide 
is  given  off  from  the  lungs  just  as  it  is  from  a  fire,  and  the 
fact  was  demonstrated  by  means  of  a  simple  experiment. 
It  is  a  waste-product  of  the  processes  going  on  in  the 
animal  body.  Just  as  it  cannot  support  combustion,  so 
also  it  cannot  support  respiration.  It  is  not  poisonous 
any  more  than  water  is;  but  it  cannot  supply  the  oxygen 
which  is  needed  for  breathing  purposes,  and  hence  animals 
die  when  placed  in  it.  They  die  by  suffocation,  as  they 
do  in  drowning.  Any  considerable  increase  in  the  quan- 
tity of  carbon  dioxide  in  the  air  above  that  which  is 
normally  present  is  objectionable,  for  the  reason  that  it 
decreases  the  proportion  of  oxygen  in  the  air  which  is 
breathed.  It  has  been  found  that  as  much  as  5  per  cent 
of  pure  carbon  dioxide  may  be  present  in  air  without 
causing  injury  to  those  who  breathe  it.  In  a  badly- 
ventilated  room  in  which  a  number  of  people  are  collected 
and  lights  are  burning,  it  is  well  known  that  in  a  short 
time  the  air  becomes  foul,  and  bad  effects,  such  as  head- 
ache, drowsiness,  etc.,  are  produced  on  the  occupants  of 
the  room.  These  effects  have  been  shown  to  be  due,  not 
to  the  carbon  dioxide,  but  to  other  waste-products  which 
are  given  off  from  the  lungs  in  the  process  of  breathing. 
The  gases  given  off  from  the  lungs  consist  of  nitrogen, 
oxygen,  carbon  dioxide,  and  water-vapor.  Besides  these, 
however,  there  are  many  substances  in  a  fine  state  of 
division  that  contain  carbon  and  are  undergoing  decom- 
position. These  are  poisonous,  and  are  the  chief  cause  of 


THE  CYCLE  OP  CORDON  IN  NATURE.  185 

the  bad  effects  experienced  in  breathing  air  which  has 
become  contaminated  by  the  products  from  the  lungs. 
As  carbon  dioxide  is  given  off  from  the  lungs  at  the  same 
time,  the  quantity  of  this  gas  present  is  proportional  to 
the  quantity  of  the  organic  impurities.  Hence,  by  deter- 
mining the  relative  quantity  of  carbon  dioxide  it  is  possible 
to  determine  whether  the  air  of  a  room  occupied  by  human 
beings  is  fit  for  use  or  not.  As  carbon  dioxide  is  formed 
in  the  earth  wherever  an  acid  solution  comes  in  contact 
with  a  carbonate,  the  gas  is  frequently  given  off  from 
fissures  in  the  earth.  It  is  hence  not  infrequently  found 
in  old  wells  that  have  not  been  in  use  for  some  time,  and 
deaths  have  been  caused  by  descending  into  these  wells  for 
the  purpose  of  repairing  them.  The  gas  is  also  frequently 
met  with  in  mines,  and  is  called  choke-damp  by  the  miners. 
The  miners  are  aware  that  after  an  explosion  caused  by 
fire-damp  there  is  danger  of  death  from  choke-damp.  The 
reason  is  simple.  When  fire-damp,  or  marsh-gas,  explodes 
with  air  the  carbon  is  converted  into  choke-damp,  or 
carbon  dioxide,  and  the  hydrogen  into  water.  Air  in 
which  a  candle  will  not  burn  is  not  fit  for  breathing 
purposes. 

The  Cycle  of  Carbon  in  Nature. — The  part  played  by 
carbon  dioxide  in  nature  is  extremely  important  and  in- 
teresting. The  carbon  of  living  things  is  obaitned  from 
carbon  dioxide,  and  returns  to  this  form  when  life  ceases. 
All  living  things  contain  carbon  as  an  essential  constituent. 
Whence  comes  this  carbon  ?  Animals  eat  either  the 
products  of  plant-life  or  other  animals  which  derive  their 
sustenance  from  the  vegetable  kingdom.  The  food  of 
animals  comes,  then,  either  directly  or  indirectly  from 
plants.  But  plants  derive  their  sustenance  largely  from 
the  carbon  dioxide  of  the  air.  The  plants  have  the  power 
to  decompose  the  gas  with  the  aid  of  the  direct  light  of 


1 86  INTRODUCTION   TO  CHEMISTRY. 

the  sun,  and  they  then  build  up  the  complex  compounds 
of  carbon  which  form  their  tissues,  using  for  this  purpose 
the  carbon  of  the  carbon  dioxide  which  they  have  decom- 
posed. Many  of  these  compounds  are  fit  for  food  for 
animals;  that  is  to  say,  they  are  of  such  composition  that 
the  forces  at  work  in  the  animal  body  are  capable  of  trans- 
forming them  into  animal  tissues,  or  of  oxidizing  them, 
and  thus  keeping  the  temperature  of  the  body  up  to  the 
necessary  point.  That  part  of  the  food  which  undergoes 
oxidation  in  the  body  plays  the  same  part  as  fuel  in  a  stove. 
It  is  burned  up  with  an  evolution  of  heat,  the  carbon  being 
converted  into  carbon  dioxide,  which  is  given  off  from  the 
lungs.  From  fires  and  from  living  animals  carbon  dioxide 
is  returned  to  the  air,  where  it  again  serves  as  food  for  the 
plants.  When  the  life-process  stops  in  the  animal  or 
plant,  decomposition  begins;  and  the  final  result  of  this, 
under  ordinary  circumstances,  is  the  conversion  of  the 
carbon  into  carbon  dioxide. 

Plants  and  Animals  as  Storehouses  of  Energy. — Under 
the  influence  of  life  and  sunlight  carbon  dioxide  is,  then, 
converted  in  the  plant  into  compounds  containing  carbon 
which  are  stored  up  in  the  plant.  These  compounds  are 
capable  of  burning,  and  thus  giving  heat;  or  some  of  them 
may  be  used  as  food  for  animals,  assuming  other  forms 
under  the  influence  of  the  life-process  of  the  animals.  As 
long  as  life  continues,  plants  and  animals  are  storehouses 
of  energy.  When  death  occurs,  the  carbon  compounds 
pass  back  to  the  form  of  carbon  dioxide;  the  energy  which 
was  stored  up  is  lost.  The  power  to  do  work  which  the 
carbon  compounds  of  plants  and  animals  possess  comes 
from  the  heat  of  the  sun.  It  takes  a  certain  quantity  of 
this  heat,  operating  under  proper  conditions,  to  decompose 
a  certain  quantity  of  carbon  dioxide  and  elaborate  the 
compounds  contained  in  the  plants.  When  these  com- 


CARBONIC  ACID  AND  CARBONATES.  187 

pounds  arc  burned  they  give  out  the  heat  which  was 
absorbed  in  their  formation  during  the  growth  of  the 
plants.  These  compounds  are  said  to  possess  chemical 
energy.  This  has  its  origin  in  heat,  and  is  capable  of 
reconversion  into  heat.  The  transformation  of  the  energy 
of  the  sun's  heat  into  chemical  energy  lies  at  the  founda- 
tion of  all  life.  As  the  heat  of  the  sim  acting  upon  the 
'"  great  bodies  of  water  and  on  the  air  gives  rise  to  the  move- 
ments of  water  which  are  essential  to  the  existence  of  the 
world  as  it  is,  so  the  action  of  the  sun's  rays  011  carbon 
'dioxide,  in  the  presence  of  the  delicate  mechanism  of  the 
leaf  of  the  plant,  gives  rise  to  those  changes  in  the  forms 
of  combination  of  the  element  carbon  which  accompany 
the  wonderful  process  of  life. 

Carbonic  Acid  and  Carbonates, — A  solution  made  by 
passing  carbon  dioxide  into  water  has  a  slightly  acid 
reaction.  [Try  it.]  It  will  act  upon  solutions  of  bases 
and  form  salts.  The  formula  of  the  sodium  salt  formed 
fti  this  way  has  been  shown  to  be  Na2C03;  that  of  the 
potassium  salt,  K2C03 ,  etc.  These  salts  are  plainly  derived 
from  an  acid,  H2CO, ,  which  is  carbonic  acid.  It  is  prob- 
able that  the  ions  of  this  acid  are  contained  in  the  solution 
of  carbon  dioxide  in  water.  These  are,  however,  easily 
rearranged  into  carbon  dioxide  and  water: 

H  +  H  +  CO,  =  H20  +  C02. 

When  carbon  dioxide  acts  upon  a  base  it  forms  a  salt. 
Thus,  with  potassium  hydroxide  or  calcium  hydroxide  the 
action  which  takes  place  is  represented  thus : 

2KOH  +  CO,  =  K2C03  +  H20; 
Ca(OH)2  +  C02  =  CaC03  -f  H20. 

With  the  acid  the  action  would  take  place  as  represented 
thus: 

2KOH  +  H2C03  =  K2003  +  2H20; 
Ca(OH)2  -f  H2C03  =  CaCO,  +  2H20. 


1 88  INTRODUCTION    TO  CHEMISTRY. 

EXPERIMENT  93. — Pass  carbon  dioxide  into  a  solution  of  caustic 
potash  until  it  will  absorb  no  more.  Add  an  acid  to  some  of  this 
solution  and  convince  yourself  that  the  gas  given  off  is  carbon 
dioxide.  Write  the  equations  representing  the  reactions  which 
take  place  on  passing  the  carbon  dioxide  into  the  solution  of 
caustic  potash,  and  on  adding  an  acid  to  the  resulting  solution. 
What  evidence  have  you  that  the  gas  given  off  is  carbon  dioxide  ? 

EXPERIMENT  94. — Pass  carbon  dioxide  for  a  short  time  into  50 
to  100  cc.  clear  lime-water.  Filter  off  the  white  insoluble  sub- 
stance. Try  the  action  of  a  little  acid  on  it.  What  evidence  have 
you  that  it  is  calcium  carbonate  ?  How  could  you  easily  distin- 
guish between  lime-water  and  a  solution  of  caustic  potash. 

Solution  of  Calcium  Carbonate  in  Water  containing 
Carbon  Dioxide. — Althoguh  when  carbon  dioxide  is  passed 
into  lime-water  calcium  carbonate  is  at  first  precipitated, 
the  calcium  carbonate  dissolves,  and  the  solution  finally 
becomes  clear,  if  the  gas  is  passed  through  it  for  some 
time.  Water  alone  does  not  dissolve  calcium  carbonate, 
but  water  containing  carbon  dioxide  does.  If  this  solution 
is  heated,  the  carbon  dioxide  is  driven  off  and  the  calcium 
carbonate  is  again  thrown  down.  Natural  waters  which 
flow  over  limestone  take  up  more  or  less  calcium  carbonate 
by  virtue  of  the  carbon  dioxide  which  they  absorb  from  the 
air  and  the  soil.  Such  waters,  which  are  called  hard 
waters,  are  in  the  condition  of  the  solution  of  calcium  car- 
bonate above  referred  to.  When  heated,  the  calcium 
carbonate  is  deposited.  This  is  frequently  noticed  in  the 
deposits  in  boilers  and  other  vessels  in  which  hard  water  is 
boiled. 

EXPERIMENT  95. — Pass  carbon  dioxide  first  through  a  little 
water  to  wash  it,  and  then  into  50  to  100  cc.  clear  lime-water. 
At  first  the  insoluble  carbonate  will  come  down,  as  in  Experiment 
94  ;  but  soon  it  will  begin  to  dissolve,  and  finally  an  almost  clear 
solution  will  be  obtained.  Heat  this  solution,  and  the  insoluble 
carbonate  will  again  appear. 

Carbon  Monoxide,  CO. — When  a  substance  containing 
carbon  burns  in  an  insufficient  supply  of  air, — as,  for 


CARBON  MONOXIDE.  189 

example,  when  the  draught  in  a  furnace  is  not  strong 
enough  to  remove  the  products  of  combustion  and  supply 
fresh  air, — the  oxidation  of  the  carbon  is  not  complete, 
and  the  product,  instead  of  being  carbon  dioxide,  is  carbon 
monoxide,  CO.  This  substance  can  also  be  made  by 
extracting  oxygen  from  carbon  dioxide.  It  is  only  neces- 
sary to  pass  the  dioxide  overheated  carbon,  when  reaction 
takes  place  as  represented  thus : 

C0.2  +  C  =  200. 

This  method  of  formation  is  illustrated  in  coal-lires,  and 
can  be  well  observed  in  an  open  grate.  The  air  has  free 
access  to  the  coal,  and  at  the  surface  complete  oxidation 
takes  place.  But  that  part  of  the  carbon  dioxide  which  is 
formed  at  the  lower  part  of  the  grate  is  drawn  up  through 
the  heated  coal  and  is  partly  reduced  to  carbon  monoxide. 
When  the  monoxide  escapes  from  the  upper  part  of  the 
grate  it  again  combines  with  oxygen,  or  burns,  giving  rise 
to  the  characteristic  blue  flame  always  noticed  above  a  mass 
of  burning  coal.  Should  anything  occur  to  prevent  free 
access  of  air,  carbon  monoxide  may  easily  escape  complete 
oxidation. 

It  is  also  formed  by  passing  water  over  highly  heated 
carbon,  when  this  reaction  takes  place : 

0  +  H20  =  CO  +  2H. 

This  is  the  reaction  that  is  made  use  of  in  the  manu- 
facture of  "  water-gas."  The  gas  thus  obtained  is  a  mix- 
ture of  hydrogen  and  carbon  monoxide.  Before  use  it  is 
enriched  by  the  addition  of  hydrocarbons  from  petroleum. 

Preparation  of  Carbon  Monoxide. — The  easiest  way  to 
make  carbon  monoxide  is  to  heat  oxalic  acid,  C2H204 ,  with 
five  to  six  times  its  weight  of  concentrated  sulphuric  acid. 
The  change  is  represented  thus : 

C3H204  =  C02  +  CO  +  H20. 


19°  INTRODUCTION    TO   CHEMISTRY. 

Both  carbon  dioxide  and  monoxide  are  formed.  Both 
are  gases.  In  order  to  separate  them  the  mixture  is  passed 
through  a  solution  of  caustic  soda,  which  takes  up  the 
carbon  dioxide  [forming  what  ?]  and  allows  the  monoxide 
to  pass. 

EXPERIMENT  96. —  Carbon  monoxide  is  poisonous  and  must  not 
be  inhaled. — Put  10  grams  crystallized  oxalic  acid  and  50-60  grams 
concentrated  sulphuric  acid  in  an  appropriate-sized  flask.  Con- 
nect with  two  Woulff's  flasks  containing  a  solution  of  caustic  soda. 
Heat  the  contents  of  the  flask  gently.  Collect  the  gas  over  water 
in  several  vessels.  Set  fire  to  some,  and  notice  the  characteristic, 
blue  flame.  What  is  formed  when  carbon  monoxide  burns  in  the 
air  ?  Introduce  the  flame  for  a  moment  into  a  flask  containing 
a  little  clear  lime-water.  What  effect  is  produced  ? 

Properties  of  Carbon  Monoxide, — Carbon  monoxide  is  a 
colorless,  tasteless,  inodorous  gas,  insoluble  in  water.  It 
burns  with  a  pale-blue  flame,  forming  carbon  dioxide.  It 
is  exceedingly  poisonous  when  inhaled.  Hence  it  is  very 
important  that  it  should  not  be  allowed  to  escape  into 
rooms  occupied  by  human  beings.  Death  is  sometimes 
caused  by  the  gases  from  coal-stoves.  The  most  dangerous 
of  these  gases  is  carbon  monoxide.  A  pan  of  smoulder- 
ing charcoal  gives  off  this  gas,  the  poisonous  character  of 
which  is  well  known.  It  has  been  used  to  some  extent 
for  the  purpose  of  suicide.  The  poisonous  character  of 
carbon  monoxide  has  led  to  a  great  deal  of  discussion  and 
to  some  legislation  on  the  subject  of  "water-gas."  The 
question  has  been  repeatedly  raised  whether  the  manufac- 
ture of  the  gas  should  be  permitted.  There  is  no  doubt 
of  the  fact  that  it  is  a  dangerous  substance;  and  that  it 
should  not  be  allowed  to  escape  into  the  air  of  rooms  is 
obvious.  With  proper  precautions,  however,  there  seems 
to  be  no  good  reason  why  it  should  not  be  used,  although 
it  is  somewhat  more  poisonous  than  coal-gas. 

At  high  temperatures  carbon  monoxide  combines  readily 
with  oxygen,  and  is  hence  a  good  reducing  agent.  In  the 


ILLUMINATION,  FLAME,  BLOWPIPE,  ETC.  191 

reduction  of  iron  from  its  ores,  the  carbon  monoxide 
formed  in  the  blast-furnace  plays  an  important  part  in  the 
reducing  process. 

EXPERIMENT  97. — Pass  carbon  monoxide  over  some  ht?ated  cop- 
per oxide  contained  in  a  hard-glass  tube.  Is  the  oxide  reduced  ? 
How  do  you  know  ?  Is  carbon  dioxide  formed  ?  What  evidence 
have  you  ?  Was  the  carbon  monoxide  used  free  of  carbon  diox- 
ide? If  not,  what  evidence  have  you  that  carbon  dioxide  is 
formed  in  this  experiment  ? 

Illumination,  Flame,  Blowpipe,  etc, — As  the  substances 
used  for  illumination  contain  carbon,  and  the  chemical 
processes  involved  consist  largely  in  the  oxidation  of  the 
carbon  of  these  compounds,  this  is  an  appropriate  place  to 
take  up  the  subject  of  illumination,  and  also  that  of  flame 
and  the  blowpipe. 

In  all  ordinary  kinds  of  illumination  flames  are  the 
immediate  source  of  the  light.  Whether  illuminating-gas, 
a  lamp,  or  a  candle  is  used,  the  light  comes  from  a  flame. 
In  the  first  case,  the  gas  is  burned  directly;  in  the  case  of 
the  lamp,  the  oil  is  first  drawn  up  the  wick,  then  converted 
into  a  gas,  and  this  burns;  while,  finally,  in  the  case  of  the 
candle,  the  solid  material  of  the  candle  is  first  melted,  then 
drawn  up  the  wick,  converted  into  gas,  and  the  gas  burns, 
forming  the  flarne.  In  each  case,  then,  there  is  a  burning 
gas,  and  this  burning  gas  is  called  a  flame. 

Illuminating-gas. — Two  kinds  of  illuminating-gas  are 
now  made,  water-gas  and  coal-gas.  The  method  of  prep- 
aration and  the  composition  of  the  former  have  been 
given.  The  latter  is  made  from  coal  by  heating  in  closed 
retorts.  When  soft  coal  is  heated  the  hydrogen  passes 
off,  partly  in  combination  with  carbon,  as  hydrocarbons, 
and  partly  in  the  free  state.  The  nitrogen  passes  oif  as 
ammonia,  and  a  large  percentage  of  the  carbon  remains 
behind  in  the  retort  in  the  uncombined  state  as  coke  (see 
page  171).  The  gases  given  off  are  purified,  and  form 


192  INTRODUCTION   TO   CHEMISTRY. 

ordinary  illuminating-gas.  One  ton  of  coal  yields  on  an 
average  10,000  cubic  feet  of  gas.  The  value  of  gas  depends 
upon  the  amount  of  light  given  by  the  burning  of  a 
definite  quantity.  It  is  measured,  by  comparing  it  with 
the  light  given  by  a  candle  burning  at  a  certain  rate.  The 
standard  candle  is  one  made  of.  spermaceti,  which  burns 
at  the  rate  of  120  grains  an  hour.  The  standard  burner 
used  for  the  gas  is  one  through  which  5  cubic  feet  of  gas 
pass  in  an  hour.  Now,  if  it  is  desired  to  determine  the 
illuminating-power  of  a  gas,  the  gas  is  passed  through  the 
standard  burner  at  the  rate  mentioned,  and  the  light 
which  it  gives  is  compared  with  the  light  given  by  the 
standard  candle.  The  comparison  is  made  by  means  of  a 
so-called  photometer.  The  illuminating-power  of  the  gas 
is  then  stated  in  terms  of  candles.  The  statement  that  the 
illuminating-power  of  a  gas  is  fourteen  candles  means  that, 
when  burning  at  the  rate  of  5  cubic  feet  an  hour,  its  flame 
gives  fourteen  times  as  much  light  as  the  standard  candle. 

Flames. — Ordinarily  when  we  speak  of  a  flame  we  mean 
a  gas  which  is  combining  with  oxygen.  The  hydrogen 
flame  is  simply  the  phenomenon  accompanying  the  act  of 
combination  of  the  two  gases  hydrogen  and  oxygen. 
Owing  to  the  fact  that  we  are  surrounded  by  oxygen,  we 
speak  of  hydrogen  as  the  burning  gas.  How  would  it  be 
if  we  were  surrounded  by  an  atmosphere  of  hydrogen  ? 
Plainly,  oxygen  would  then  be  a  burning  gas.  If  a  jet  of 
oxygen  is  allowed  to  escape  into  a  vessel  containing 
hydrogen,  a -flame  will  appear  where  the  oxygen  escapes 
from  the  jet,  if  a  light  is  applied.  This  is  an  experiment 
requiring  great  precautions,  and,  as  the  principle  can  be 
illustrated  as  well  by  means  of  illuminating-gas,  we  may 
use  this  instead.  Just  as  illuminating-gas  burns  in  an 
atmosphere  of  oxygen,  so  oxygen  "burns "in  an  atmos- 
phere of  illuminating-gas. 


KINDLING  TEMPERATURE  OF  GASES. 


'93 


EXPERIMENT  98. — Break  off  the  neck  of  a  good-sized  retort ;  fit 
a  perforated  cork  to  the  small  end  ;  pass  a  piece  of  glass  tube 
through  the  cork  and  connect  by  means  of  rubber  hose  with  an 
outlet  for  illuminating  gas.  Fix  the  apparatus  in  position,  as  shown 
in  Fig.  44.  Turn  the  gas  on,  and  when  the  air  is  driven  out  of 
the  retort-neck,  light  the  gas.  The  neck  is  now  filled  with  illu- 
minating-gas, and  the  gas  is  burning  at  the  mouth  of  the  vessel. 
If  now  a  platinum  jet  from  which  oxygen  is  issuing  is  passed  up 


FIG.  44. 

into  the  gas  the  oxygen  will  take  fire,  and  a  flame  will  appear 
where  the  oxygen  escapes  from  the  jet.  The  oxygen  burns  in  the 
atmosphere  of  coal-gas. 

Kindling-temperature  of  Gases. — In  studying  the  action 
of  oxygen  upon  other  substances,  we  learned  that  it  is 
necessary  that  each  of  these  substances  should  be  raised  to 
a  certain  temperature  before  it  will  burn.  This  statement 
is  as  true  of  gases  as  of  other  substances.  When  a  current 
of  hydrogen  is  allowed  to  escape  into  the  air  or  into 
oxygen,  no  action  takes  place  unless  it  is  heated  up  to  its 
burning-temperature,  when  it  takes  fire  and  continues  to 
burn,  as  the  burning  of  one  part  of  the  gas  heats  up  the 
part  that  follows  it,  and  hence  the  gas  is  heated  up  to  the 
burning-temperature  as  fast  as  it  escapes  into  the  air.  If 
the  gas  should  be  cooled  down  even  very  slightly  below 


194  INTRODUCTION  TO  CHEMISTRY. 

this  temperature,  it  would  be  extinguished.     This  is  shown 
in  a  very  striking  manner  by  the  following  experiments: 

EXPERIMENT  99. — Light  a  Bunsen-burner.  Bring  down  upon 
the  flame  a  piece  of  fine  brass  or  iron-wire  gauze.  There  is  no 
flame  above  the  gauze.  That  the  gas  passes  through  unburned 
can  be  shown  by  applying  a  light  just  above  the  outlet  of  the 
burner  and  above  the  gauze.  The  gas  will  take  fire  and  burn. 
By  simply  passing  through  the  thin  wire  gauze,  then,  the  gas  is 
cooled  down  below  its  burning-temperature,  and  does  not  burn 
unless  it  is  heated  up  again.  Turn  on  a  Bunsen  burner.  Do  not 
light  the  gas.  Hold  a  piece  of  wire  gauze  one  and  a  half  to 
two  inches  above  the  outlet.  Apply  a  lighted  match  above  the 
gauze,  when  the  gas  will  burn  above  the  gauze,  but  not  below  it. 
Here  again  the  heat  necessary  to  raise  the  temperature  of  the  gas 
to  the  burning-temperature  cannot  be  communicated  through  the 
gauze.  If  in  either  of  the  above-described  experiments  the  gauze 
is  held  in  position  for  a  time,  it  will  probably  become  so  highly 
heated  that  the  gas  on  the  one  side  where  there  is  no  flame  will 
be  raised  to  the  burning-temperature.  The  instant  that  point  is 
reached  the  flame  becomes  continuous. 

Safety-lamp, — The  principle  illustrated  in  the  preced- 
ing experiments  is  utilized  in  the  miner's 
safety-lamp.  One  of  the  dangers  which 
the  coal-miner  has  to  encounter  is  the 
occurrence  of  fire-damp,  or  methane, 
CH4 ,  which  with  air  forms  an  explosive 
mixture.  The  explosion  can  be  brought 
about  only  by  contact  of  flame  with 
the  mixture.  In  order  to  avoid  the 
contact,  the  flame  of  the  safety-lamp  is 
surrounded  by  wire  gauze,  as  shown  in 
Fig.  45.  When  a  lamp  of  this  kind  is 
brought  into  an  explosive  mixture  of 
marsh-gas  and  air,  the  mixture  passes 
through  the  wire  gauze  and  comes  in  con- 
tact with  the  flame,  and  a  slight  explosion 
occurs  inside  the  gauze,  but  the  flame  of  the  burning 


STRUCTURE  OF  FL4MES.  195 

gas  inside  the  wire  gauze  cannot  pass  through  and 
raise  the  temperature  of  the  gas  outside  to  the  burning- 
temperature.  Hence  no  serious  explosion  can  take  place. 
The  flickering  of  the  flame  of  the  lamp,  and  the  occur- 
rence of  small  explosions  inside,  furnish  the  miner  with 
the  information  that  he  is  in  a  dangerous  atmosphere. 

Structure  of  Flames, — The  hydrogen  flame  consists  of  a 
thin  envelope  of  burning  hydrogen  enclosing  unburned 
gas,  and  surrounded  by  water-vapor,  which  is  the  product 
of  the  combustion.  The  structure  of  other  flames  depends 
upon  the  complexity  of  the  gases  burned  and  the  condi- 
tions under  which  the  burning  takes  place.  In  general, 
a  flame  consists  of  an  outer  envelope  of  gas  combining 
with  oxygen,  and  hence  hot,  and  an  inner  part  which 
contains  unburned  gas,  which  is  relatively  cool.  A  part 
of  the  unburned  gas  is,  however,  hot,  and  it  would  com- 
bine with  oxygen  were  it  not  for  the  fact  that  it  is 
surrounded  by  an  envelope  which  prevents  access  of  air. 
The  outer  hot  part  of  the  flame  is  called  the  oxidizing 
flame,  because  it  presents  conditions  favorable  to  the 
oxidation  of  substances  introduced  into  it.  The  inner 
hot  part  is  called  the  reducing  flame,  because  it  consists  of 
highly-heated  substances  which  have  the  power  to  combine 
with  oxygen,  and  hence  many  compounds  containing 
oxygen  lose  it,  or  are  reduced,  when  introduced  into  this 
part  of  the  flame.  The  hottest  part  of  the  flame  is  at  the 
extreme  top.  Here  oxidation  is  taking  place  most  ener- 
getically. The  hottest  part  of  the  unburned  gases  is  at 
the  tip  of  the  dark  central  part  of  the  flame.  In  the  flame 
of  a  Bunsen  burner  the  two  parts  can  be  easily  dis- 
tinguished. The  dark  central  part  of  the  flame  ex- 
tends for  some  distance  above  the  outlet  of  the  burner. 
If  the  holes  at  the  base  of  the  burner  are  partly  closed, 
the  tip  of  the  central  part  of  the  flame  becomes  luminous. 


196  INTRODUCTION    TO   CHEMISTRY. 

This  luminous  tip  is  most  efficient  for  the  purpose  of 
reduction.  The  principal  parts  of  the  flame  are 
those  marked  in  Fig.  46.  B  is  the  central  cone 
of  unburned  gas.  0  is  the  luminous  tip,  the 
best  part  of  the  flame  for  reduction.  A  is  the 
envelope  of  burning  gas.  This  is  further  sur- 
rounded by  a  non-luminous  envelope  consisting 
_c  of  the  products  of  combustion,  carbon  dioxide 
and  water-vapor.  Certain  metals  placed  in  the 
upper  end  of  the  flame  take  up  oxygen,  because 
they  are  highly  heated  in  the  presence  of  oxy- 
gen. Certain  oxides  lose  their  oxygen  when 
placed  in  the  tip  of  the  central  cone,  because 
the  gases  are  here  heated  to  the  temperature 
at  which  they  have  the  power  to  combine  with 

oxygen. 

Blowpipe. — The  oxidizing  and  reducing  flames  are  fre- 
quently utilized  in  the  laboratory.  For  the  purpose  of 
increasing  their  efficiency  a  blowpipe  is  used.  This  is  a 
tube  through  which  air  is  blown  into  a  flame  by  means  of 
the  mouth.  It  is  usually  constructed  in  the  shape  shown 
in  Fig.  47.  At  the  smaller  end,  which  is  placed  in  the 


FIG.  47. 

flame,  there  is  usually  a  small  tube  of  platinum.  The 
blowpipe  may  be  used  with  the  flame  of  a  candle,  an 
alcohol-lamp,  or  a  gas-lamp.  It  is  most  frequently  used 
with  the  gas-lamp.  A  piece  of  brass  tubing  which  fits 
snugly  in  the  tube  of  a  Bunsen  burner  is  cut  off  and 
hammered  together  so  as  to  leave  a  narrow  slit-like  open- 
ing. This  tube  is  then  slipped  into  the  burner,  as  shown 


BLOWPIPE. 


197 


in  Fig.  48.  It  reaches  to  the  bottom  of  the  burner,  and 
thus  cuts  off  the  supply  of  air  which  usually  enters  the 
holes  at  the  base.  The  gas  is  now  lighted  and  the  flow 
so  regulated  that  there  is  a  small  flame  about  1^  to 
2  inches  high.  The  tip  of  the  blowpipe  is  placed  on  the 
slit  of  the  burner  in  the  flame,  so  that  it  extends  about 
one  third  .the  way  across  it,  as  shown  in  Fig.  49.  By 
blowing  regularly  and  not  too  violently  through  the  pipe 
the  flame  is  forced  down  in  the  same  direction 
as  the  end-piece  of  the  blowpipe,  and  the  slant 
of  the  burner-slit.  Under  proper  conditions 
it  separates  sharply  into  a  central  blue  part  and 


FIG.  48.  Fro.  49.  FIG.  50. 

an  outer  part  of  another  color.  The  direction  and  lines 
of  division  of  the  flame  are  indicated  in  Fig.  50.  The 
extreme  outer  tip  A  is  the  most  efficient  oxidizing  flame. 
The  tip  B  of  the  inner  blue  part  is  the  most  efficient 
reducing  flame. 

The  use  of  the  blowpipe  is  illustrated  by  the  following 
experiments : 

EXPERIMENT  100.— Select  a  piece  of  charcoal  about  4  inches 
long  by  1  inch  wide  and  1  inch  thick,  with  one  surface  plane.* 
Near  the  end  of  the  plane  surface  make  a  cavity  by  pressing  the 
edge  of  a  small  coin  against  it,  and  turning  it  completely  around 
a  few  times.  Mix  together  equal  small  quantities  of  dry  sodium 
carbonate  and  lead  oxide.  Put  a  little  of  the  mixture  in  the 

*  Pieces  of  charcoal  prepared  for  blowpipe  work  can  be  bought 
from  dealers  in  chemical  apparatus  at  small  cost. 


198  INTRODUCTION    TO   CHEMISTRY. 

cavity  in  the  charcoal,  and  heat  it  in  the  reducing  flame  pro- 
duced by  the  blowpipe.  In  a  short  time  globules  of  metallic 
lead  will  be  seen  in  the  molten  mass.  After  cooling,  scrape  the 
solidified  substance  out  of  the  cavity  in  the  charcoal.  Put  it  into 
a  small  mortar,  treat  it.  with  a  little  water,  and,  after  breaking 
it  up  and  allowing  as  much  as  possible  to  dissolve,  pick  out  the 
metallic  beads.  [Is  it  malleable  or  brittle  ?  Is  metallic  lead 
malleable  or  brittle  ?  Is  it  dissolved  by  hydrochloric  acid  ?  Is 
lead  soluble  in  hydrochloric  acid?  Is  it  soluble  in  nitric  acid  ? 
Is  lead  soluble  in  nitric  acid  ?]  The  action  of  the  acids  may  be 
tried  by  putting  the  bead  on  a  small  dry  watch-glass  and  adding 
a  few  drops  of  the  acid.  [Does  the  substance  act  like  lead  ? 
What  has  become  of  the^  oxygen  with  which  the  lead  was  com- 
bined in  the  oxide  ?  Is  there  any  advantage  in  having  a  support 
of  charcoal  for  this  experiment  ?] 

EXPERIMENT  101. — Heat  a  small  piece  of  metallic  lead  on  char- 
coal in  the  oxidizing  flame  of  the  blowpipe.  Notice  the  formation 
of  the  oxide,  which  forms  a  coating  or  film  on  the  charcoal  in  the 
neighborhood  of  the  metal.  [Is  there  any  analogy  between  this 
process  and  the  burning  of  hydrogen  ?  In  what  does  the  analogy 
consist  ?  What  differences  are  there  between  the  two  processes  ?  ] 

Use  of  the  Blowpipe  in  Analysis. — Some  oxides  are 
easily  reduced  when  heated  in  the  reducing  flame.  Others 
are  not.  The  composition  of  a  substance  can  often  be 
determined  by  heating  it  in  the  blowpipe  flame  and 
noticing  its  conduct.  Some  metals  are  easily  oxidized  in 
the  oxidizing  flame.  Some  form  characteristic  films  of 
oxides  on  the  charcoal,  and  in  some  cases  it  is  possible  to 
detect  the  presence  of  certain  substances  by  noticing  the 
color  of  the  film  of  oxide.  The  blowpipe  is  therefore  of 
great  value  as  affording  a  means  of  detecting  the  presence 
of  certain  elements  in  mixtures  or  compounds  of  unknown 
composition.  The  chemical  principles  involved  in  its  use 
will  be  clear  from  what  has  already  been  said. 

Causes  of  the  Luminosity  of  Flames, — It  is  evident  from 
what  has  been  seen  that  flames  vary  greatly  in  their  light- 


CAUSES   OF   THE   LUMINOSITY   OF  FLAMES.         1 99 

giving  power.  The  hydrogen  flame,  for  example,  gives 
practically  no  light.  This  is  also  the  case  with  the  flame 
of  the  Bunsen  burner;  while,  on  the  other  hand,  the  flame 
of  illuminating-gas  burning  under  ordinary  circumstances, 
and  that  o£  a  candle,  etc.,  give  light.  [To  what  is  the 
difference  due  ?]  There  are  several  causes  which  operate 
to  make  a  flame  give  light,  and  vice  versa.  In  the  first 
place,  if  a  solid  substance  which  does  not  burn  up  is  intro- 
duced into  a  non-luminous  flame,  a  part  of  the  heat 
appears  as  light.  This  is  seen  when  a  spiral  of  platinum 
wire  is  introduced  into  a  hydrogen  flame.  It  has  also  been 
shown  by  introducing  a  piece  of  lime  into  the  hot  non- 
luminous  flame  of  the  oxyhydrogen  blowpipe.  A  similar 
cause  operates  in  ordinary  gas-flames  to  make  them 
luminous.  Particles  of  unburned  carbon  are  always  pres- 
ent, as  can  be  shown  by  putting  a  piece  of  porcelain  or 
any  solid  substance  into  the  flame,  when  there  will  be 
deposited  011  it  a  layer  of  soot,  which  consists  mainly  of 
finely-divided  carbon.  In  the  flame  these  particles  of 
carbon  are  heated  to  the  temperature  at  which  they  give 
light.  Again,  it  has  been  found  that  the  same  candle  gives 
more  light  at  the  level  of  the  sea  than  it  does  when  at  the 
top  of  a  high  mountain,  as  Mont  Blanc,  on  which  the  ex- 
periment was  actually  performed.  This  is  partly  due  to  a 
difference  in  the  density  of  the  gases.  Naturally,  the 
denser  the  gas  the  more  active  the  combustion,  the  greater 
the  heat,  and  the  greater  the  light.  This  last  statement 
ceases  to  be  true  when  the  oxidation  becomes  sufficient  to 
burn  up  all  the  solid  particles  of  carbon  in  the  flame.  If 
gases  which  in  burning  give  light  are  cooled  dowli  befcro 
they  are  burned,  the  luminosity  is  diminished,  and,  con- 
versely, non-luminous  flames  may  be  rendered  luminous 
by  heating  the  gases  before  burning  them.  AVhen  gases 
which  give  luminous  flames  are  diluted  to  a  sufficient 
extent  with  neutral  gases,  such  as  nitrogen  and  carbon 


200  INTRODUCTION    TO   CHEMISTRY. 

dioxide,  which  neither  burn  nor  support  combustion,  they 
become  non-luminous.  It  has  lately  been  shown  that  the 
formation  and  decomposition  of  acetylene  (which  see)  in 
flames  is  an  important  factor  in  the  luminosity  of  flames. 

Bunsen  Burner. — All  the  statements  made  in  regard  to 
the  causes  of  the  luminosity  of  flames  are  based  upon 
carefully-performed  experiments.  These  experiments, 
however,  cannot  be  easily  repeated  by  the  student  in  the 
laboratory  in  a  satisfactory  way.  One  constant  reminder 
of  the  possibility  of  rendering  a  luminous  flame  non- 
luminous,  and  a  non-luminous  flame  luminous,  is  furnished 
by  the  burner  universally  used  in  chemical  laboratories, 
and  called,  after  the  inventor,  the  Bunsen  burner.  The 
construction  of  this  burner  is  easily  understood.  It  con- 
sists of  a  base  and  an  upper  tube.  The  base  is  connected 
by  means  of  a  rubber  tube  with  the  gas-supply.  The  gas 
escapes  from  a  small  opening  in  the  base,  and  passes  up 
through  the  tube.  At  the  lower  part  of  the  tube  there  are 
two  holes,  which  can  be  opened  or  closed  by  turning  a  ring 
with  two  corresponding  holes  in  it.  When  the  gas  is 
turned  on,  it  is  lighted  at  the  top  of  the  tube.  Air  is  at 
the  same  time  drawn  through  the  holes  at  the  base.  The 
result  is  that  the  flame  is  practically  non-luminous.  If 
the  ring  at  the  base  is  turned  sc  that  the  air-holes  are 
closed,  the  flame  becomes  luminous.  The  advantage  of 
the  non-luminous  flame  for  laboratory  use  consists  in  the 
fact  that  it  does  not  deposit  soot,  and,  at  the  same  time, 
it  does  give  a  good  heat. 

[Could  the  hydrogen  flame  deposit  soot  ?] 
The  non-luminosity  of  the  flame  of  the  Bunsen  burner 
appears  to  be  due  to  several  causes:  (1)  Dilution  of  the 
gases  by  means  of  the  nitrogen  of  the  air;  (2)  Cooling  of 
the  gases  by  the  entrance  of  the  air;  (3)  Burning  of  the 
solid  particles  by  the  aid  of  the  oxygen  of  the  air  admitted 
to  the  interior  of  the  flame. 


CYANOGEN-HYDROCYANIC  ACID.  201 

Cyanogen,  C8N2.  —  Carbon  does  not  combine  with  ni- 
trogen under  ordinary  circumstances.  If,  however,  they 
are  brought  together  at  very  high  temperatures  in  the 
presence  of  metals,  they  combine  to  form  compounds 
known  as  cyanides.  Thus,  when  nitrogen  is  passed  over 
a  highly-heated  mixture  of  carbon  and  potassium  car- 
bonate, K2C03,  the  compound  potassium  cyanide,  KCN, 
is  formed.  Carbon  containing  nitrogen,  as  animal  char- 
coal, when  ignited  with  potassium  carbonate,  reduces  the 
potassium  carbonate,  forming  potassium,  and  this  causes 
the  carbon  and  nitrogen  to  combine,  forming  potassium 
cyanide.  When  refuse  animal  substances,  such  as  blood, 
horns,  claws,  hair,  wool,  etc.,  are  heated  together  with 
potassium  carbonate  and  iron,  a  substance  known  as 
potassium  ferrocyanide,  or  yellow  prussiate  of  potash, 
4KCN.Fe(CN)2  +  3H20,  is  formed.  When  this  is  simply 
heated  it  decomposes,  yielding  potassium  cyanide.  It  is 
not  a  difficult  matter  to  make  mercuric  cyanide,  Hg(CN)2, 
from  the  potassium  compound.  By  heating  mercuric 
cyanide  it  breaks  down,  yielding  metallic  m'ercury  and 
cyanogen  gas: 

Hg(CN)2  =  Hg  +  C.N, 

[What  analogy  is  there  between  this  reaction  and  that 
which  takes  place  when  mercuric  oxide  is  heated  ?] 

Cyanogen  is  a  colorless  gas.  It  receives  its  name  from 
the  fact  that  some  of  its  compounds  are  blue  (Kvavos, 
blue).  It  is  easily  soluble  in  water  and  alcohol.  It  is 
extremely  poisonous. 

Hydrocyanic  Acid,  Prussia  Acid,  HCN.  —  This  acid 
occurs  in  nature  in  combination  with  other  substances, — - 
in  bitter  almonds,  the  leaves  of  the  cherry,  laurel,  etc.  It 
is  prepared  by  treating  the  cyanides  with  sulphuric  or 


202  INTRODUCTION   TO  CHEMISTRY. 

hydrochloric  acid.     Thus,  by  treating  potassium  cyanide 
with  sulphuric  acid  this  reaction  takes  place: 

2KCN  +  H2S04  =  K2S04  +  2HCK 

[What  reactions  already  studied  does  this  suggest  ?] 
Further,  by  treating  potassium  cyanide  with  a  solution 
of  hydrochloric  acid  in  water,  hydrocyanic  acid  is  liberated : 

KCN  +  HC1  =  KC1  +  HCN". 

[Compare  these  reactions  with  similar  reactions  already 
studied.] 

Hydrocyanic  acid  is  a  volatile  liquid  which  boils  at 
26.5°,  and  solidifies  at  —  15°.  It  has  a  very  characteristic 
odor,  resembling  that  of  bitter  almonds.  It  is  extremely 
poisonous.  It  dissolves  in  water  in  all  proportions,  and 
the  solution  is  known  as  prussic  acid. 

Both  cyanogen  and  hydrocyanic  acid  are  extremely  un- 
stable. In  the  presence  of  water,  the  nitrogen  tends  to 
combine  with  hydrogen  to  form  ammonia,  and  the  carbon 
with  oxygen  and  hydrogen  to  form  more  stable  compounds. 

Carbides  are  compounds  of  carbon  with  metallic  elements 
such  as  calcium,  aluminium.  A  good  example  is  calcium 
carbide  (see  CALCIUM). 

Summary, — Carbon  is  contained  in  all  living  things,  and 
in  their  fossil  remains.  The  number  of  compounds  which 
it  forms  is  almost  infinite.  They  are  usually  treated 
together  under  the  head  of  Organic  Chemistry. 

Carbon  is  found  in  the  atmosphere  in  the  form  of  carbon 
dioxide,  and  in  the  form  of  carbonates  it  is  widely  dis- 
tributed in  the  earth. 

Uncombined,  it  occurs  in  nature  as  diamond  and 
graphite. 

Amorphous  carbon  is  a  third  variety  of  carbon.      Char 
.coal  in  its  various  forms  is  amorphous  carbon.     It  is  made 


CARBOti- SUM  MARY.  203 

by  charring  organic  substances  which  contain  carbon, 
hydrogen,  and  oxygen.  Coke,  lamp-black,  and  bone-black 
are  other  forms  of  amorphous  carbon.  Bone-black  has 
the  power  to  extract  coloring  matters  from  solutions. 
Charcoal  has  the  power  to  absorb  gases,  and  is  used  for 
purifying  air.  It  also  absorbs  disagreeable  substances  from 
water,  and  is  used  for  the  purpose  of  purifying  water. 

Coal  is  a  form  of  carbon  found  in  nature  in  many 
varieties.  The  soft  coals  contain  more  hydrogen  than  the 
hard  coals,  which  contain  a  larger  percentage  of  carbon. 

At  ordinary  temperatures  carbon  is  a  very  inactive 
element.  At  high  temperatures  it  combines  with  oxygen 
with  avidity.  It  is  hence  a  good  reducing  agent,  and  is 
used  extensively  as  such  in  the  extraction  of  metals  from 
their  ores. 

Carbon  forms  a  large  number  of  compounds  with 
hydrogen.  These  are  the  hydrocarbons. 

Carbon  dioxide  is  formed  in  many  natural  processes,  as 
in  respiration,  combustion,  decay,  and^fermentation.  It 
is  prepared  by  treating  a  carbonate  with  an  acid.  The  gas 
given  off  is  not  carbonic  acid,  but  a  substance  which  bears 
to  the  acid  the  relation  of  an  anhydride. 

Carbon  dioxide  is  the  food  of  plants.  Plants  form  the 
food  of  animals.  Animals  give  back  carbon  dioxide  to  the 
air  in  the  process  of  breathing.  After  death  the  carbon  of 
animals  and  plants,  if  left  exposed  to  the  air,  passes  back 
largely  to  the  form  of  carbon  dioxide,  and  again  starts  on 
its  round. 

Carbon  dioxide  forms  salts  with  bases.  These  have  the 
general  formula  M2C03,  in  which  M  represents  any  univa- 
lent  metal,  such  as  potassium,  sodium,  etc.  These  are 
very  unstable,  being  decomposed  by  any  acid. 

Calcium  carbonate  is  insoluble  in  water,  but  it  dissolves 
in  water  containing  carbon  dioxide.  When  heated  the 
carbon  dioxide  is  driven  off  and  the  calcium  carbonate 


204  INTRODUCTION    TO   CHEMISTRY. 

deposited.  This  phenomenon  is  the  same  as  that  which 
gives  rise  to  the  ordinary  boiler  incrustations. 

Carbon  monoxide  is  a  poisonous  gas,  which  is  formed 
by  incomplete  oxidation  of  carbon  or  incomplete  reduction 
of  carbon  dioxide.  It  is  formed  in  ordinary  coal  fires  by 
the  passage  of  carbon  dioxide  over  hot  coal  or  charcoal. 
It  combines  readily  with  oxygen.,  and  is  hence  a  good 
reducing  agent. 

A  flame  is  a  burning  gas.  A  gas  that  burns  in  oxygen 
will  form  an  atmosphere  in  which  oxygen  will  burn.  If  a 
burning  gas  is  cooled  down  even  very  slightly  below  its 
burning-temperature,  it  is  extinguished.  In  the  miner's 
safety-lamp  the  flame  is  surrounded  by  a  piece  of  wire 
gauze.  The  gas  cannot  pass  through  this  gauze  without 
being  cooled  down  below  the  burning-temperature. 

Flames  are  made  up  of  different  parts  with  different 
properties.  The  outer  tip  is  the  hottest  part,  and  is  called 
the  oxidizing  flame.  The  tip  of  the  dark  inner  part,  con- 
sisting of  unburned  gas,  is  the  reducing  flame. 

A  luminous  flame  can  be  made  non-luminous  by  diluting 
the  burning  gas  with  neutral  gases;  by  cooling  the  gases; 
by  introducing  oxygen  into  the  gas  so  as  to  effect  complete 
oxidation  of  the  carbon. 

In  the  presence  of  metals  carbon  and  nitrogen  combine 
to  form  cyanides.  From  these,  cyanogen  and  hydrocyanic 
acid  are  obtained. 


CHAPTER   XIII. 

AVOGADRO'S    HYPOTHESIS.— MOLECULAR    WEIGHTS. 
—MOLECULAR    FORMULAS.— VALENCE. 

Avogadro's  Hypothesis. — Early  in  this  century  the  Italian 
physicist  and  chemist,  Avogadro,  occupied  himself  with 
the  study  of  the  specific  gravities  of  gaseous  substances,  and 
he  recognized  clearly  that  there  is  some  connection  between 
the  figures  representing  the  relative  weights  of  equal 
volumes  of  gases  and  those  representing  the  combining 
weights.  It  has  already  been  pointed  out  that  the  weights 
of  equal  volumes  of  hydrogen,  chlorine,  and  oxygen  bear 
to  one  another  the  same  relation  as  their  atomic  weights, 
viz.,  nearly  1  :  35.4  :  16.  This  is  noticed  in  the  case  of  other 
gases.  This  fact,  taken  together  with  others  relating  to 
the  physical  properties  of  gases,  led  Avogadro  to  the  con- 
ception that  equal  volumes  of  all  gases  under  the  same 
conditions  of  temperature  and  pressure  contain  the  same 
mimtier  of  molecules,  the  molecule  of  a  substance  being  the 
smallest  particle  of  that  substance  as  it  exists  in  the  free 
state  or  uncombined.  This  is  known  as  Avogadro's 
hypothesis.  It  has  been  tested  in  many  ways,  and  has 
always  asserted  itself  as  correct.  The  investigations  of 
both  chemists  and  physicists  have  only  tended  to  confirm 
it.  suul  at  the  present  day  it  forms  one  of  the  most  im- 
portant foundations  of  thought  in  regard  to  chemical 
phenomena. 

205 


206  INTRODUCTION    TO   CHEMISTRY. 

The  weights  of  equal  volumes  of  gases  can  be  determined 
without  difficulty.  According  to  the  hypothesis  of  Avo- 
gadro,  these  weights  bear  to  one  another  the  same  relation 
that  the  weights  of  the  molecules  of  these  substances  do. 
Take,  for  example,  those  compounds  thus  far  studied 
which  are  gases  at  ordinary  temperatures,  or  can  easily  be 
converted  into  gases  by  heat.  These  are  water,  hydro- 
chloric acid,  ammonia,  nitrous  oxide,  nitric  oxide,  marsli- 
gas,  carbon  dioxide,  carbon  monoxide,  cyanogen,  hydro- 
cyanic acid.  The  specific  gravities  of  these  substances  in 
the  form  of  gas  or  vapor  have  been  determined.  They 
are:  water,  0.6218;  hydrochloric  acid,  1.27;  ammonia, 
0.59;  nitrous  oxide,  1.53;  nitric  oxide,  1.039;  marsh-gas, 
0.559;  carbon  dioxide,  1.529;  carbon  monoxide,  0.9672; 
cyanogen,  1.8;  hydrocyanic  acid,  0.948.  These  figures 
express  the  relative  weights  of  equal  volumes  of  the  gases, 
and  they  also  express  the  relation  between  the  weights  of 
the  molecules  of  the  substances.  It  is  only  necessary  to 
adopt  some  standard  to  which  we  can  refer  the  weights  of 
other  molecules.  Hydrochloric  acid  will  serve  the  purpose. 
The  smallest  molecular  weight  that  can  be  assigned  to  this 
compound  without  making  the  atomic  weight  of  hydrogen 
less  than  unity  is  36.4,  for  hydrochloric  acid  consists  of 
1  part  by  weight  of  hydrogen  combined  with  35.4  parts  by- 
weight  of  chlorine.  Hence,  if  the  sum  of  the  weights  of 
its  atoms  or  its  molecular  weight  were  less  than  36.4,  the 
weight  of  the  atom  of  hydrogen  would  be  less  than  1.  If 
the  molecular  weight  of  hydrochloric  acid  is  36.4,  it  is  an 
easy  matter  to  calculate  the  molecular  weights  of  the 
other  substances  mentioned,  for,  according  to  Avogadro's 
hypothesis,  they  bear  to  the  molecular  weight  of  hydro- 
chloric acid  the  same  relation  that  their  specific  gravities 
bear  to  the  specific  gravity  of  hydrochloric  acid.  The 
results  of  the  calculation  are  given  in  the  subjoined  table : 


AVOGADROS  HYPOTHESIS. 


207 


Compound. 

Sp.  Gr.  of  Gas 
or  Vapor. 

Calculated 
Molec.  Weight. 

0.6218 

17.8 

Hydrochloric  acid.         ....          

1.27 

36  4 

Ammonia  

059 

16  9 

Nitrous  oxide  

1.53 

43.8 

Nitric  oxide  

1.039  • 

29.8 

0.559 

16 

Carbon  dioxide  

1.529 

43  8 

Carbon  monoxide  

0  9672 

27.7 

Cyanogen  

1  8 

51  6 

Hydrocyanic  acid  . 

0.948 

27  2 

The  figures  thus  obtained  are  relatively  correct,  provided 
always  the  hypothesis  upon  which  the  calculation  is  based' 
is  correct.  Now,  by  analysis,  it  is  found  that  in  18  parts 
by  weight  of  water  there  are  2  of  hydrogen  and  16  of  oxy- 
gen; in  36.4  parts  by  weight  of  hydrochloric  acid  there  are 
1  of  hydrogen  and  35.4  of  chlorine;  in  17  of  ammonia, 
14  of  nitrogen  and  3  of  hydrogen;  in  nitrous  oxide,  28  of 
nitrogen  and  16  of  oxygen;  in  nitric  oxide,  14  of  nitrogen 
and  16  of  oxygen;  in  marsh-gas,  12  of  carbon  and  4 
of  hydrogen;  in  carbon  dioxide,  12  of  carbon  and  32  of 
oxygen;  in  carbon  monoxide,  12  of  carbon 'and  16  of 
oxygen;  in  cyanogen,  24  of  carbon  and  28  of  nitrogen;  in 
hydrocyanic  acid,  1  of  hydrogen,  12  of  carbon,  and  14  of 
nitrogen.  Knowing  the  weights  of  the  molecules  into 
which  an  element  enters,  and  the  relative  weight  of  the 
element  present  in  these  molecules,  the  smallest  weight  of 
the  element  that  enters  into  the  composition  of  molecules 
is  selected  as  the  atomic  weight.  Thus,  the  examination 
of  all  known  oxygen  compounds  that  can  be  studied  in  the 
form  of  gas  or  vapor  shows  that  the  smallest  weight  of 
oxygen  found  in  any  molecule  is  represented  by  16,  using 
the  standard  already  adopted.  Thus,  in  water,  to  make 
up  the  molecular  weight,  18,  there  are  16  parts  by  weight 
of  oxygen  and  2  parts  by  weight  of  hydrogen;  in  nitrous 


208  INTRODUCTION   TO   CHEMISTRY. 

oxide,  28  of  nitrogen  and  16  of  oxygen;  in  carbon  dioxide, 
12  of  carbon  and  32  of  oxygen;  in  carbon  monoxide,  12  of 
carbon  and  16  of  oxygen.  The  number  16  is  therefore 
selected  as  the  atomic  weight  of  oxygen. 

The  ratio  of  the  specific  gravity  of  a  gas  to  its  molecular 
weight  is  approximately  1  :  28.88,  i.e. , 

^f=  38.88,        or        M  =  d  X  28.88, 
(I 

in  which  M  represents  the  molecular  weight  of  a  gaseous 
compound,  and  d  its  specific  gravity  as  compared  with  air 
as  the  standard..  This  gives  the  molecular  weight  very 
nearly.  The  exact  figure  to  be  adopted  is  then  determined 
by  analysis. 

Molecules  of  the  Elements. — The  acceptance  of  Avo- 
gadro's  hypothesis  leads  to  a  curious  conclusion  regarding 
the  structure  of  elementary  gases.  The  molecular  weights 
of  hydrogen,  oxygen,  chlorine,  and  nitrogen  are  found  to 
be  2,  32,  70.8,  and  28  respectively.  In  other  words,  they 
are  twice  as  great  as  their  atomic  weights.  According  to 
this,  these  gases  consist  of  molecules  which  are  twice  as 
heavy  as  their  atoms,  or,  in  other  words,  the  molecules  of 
these  elementary  gases  consist  of  two  atoms  each.  The 
same  conclusion  is  reached  in  another  way.  When  one 
volume  of  hydrogen  combines  with  one  volume  of  chlorine, 
two  volumes  of  hydrochloric  acid  are  formed.  Now,  as 
equal  volumes  of  all  gases  contain  the  same  number  of 
molecules,  if  we  assume  that  in  a  certain  volume  of 
hydrogen  there  are  100  molecules,  then  in  the  same  volume 
of  chlorine  and  of  hydrochloric  acid  there  are  also  100 
molecules.  But  from  1  volume  containing  100  molecules 
of  hydrogen  and  1  volume  containing  100  molecules  of 
chlorine  2  volumes  containing  2 00  molecules  of  hydrochloric 
acid  are  formed.  In  each  molecule  of  hydrochloric  acid 
gas  there  must  be  at  least  one  atom  of  hydrogen  and  one 


MOLECULES   OF  THE  ELEMENTS.  209 

atom  of  chlorine,  and  in  the  200  molecules  of  hydrochloric 
acid  there  must  be  200  atoms  of  hydrogen  and  200  atoms 
of  chlorine.  These  200  atoms  of  hydrogen,  however,  must 
have  been  contained  in  the  100  molecules  of  hydrogen  with 
which  we  started,  and  similarly  the  200  atoms  of  chlorine 
must  have  been  contained  in  the  100  molecules  of  chlorine. 
Therefore,  each  molecule  of  hydrogen  must  consist  of  at 
least  2  atoms  of  hydrogen,  and  each  molecule  of  chlorine 
must  consist  of  at  least  2  atoms  of  chlorine. 

A  similar  study  of  other  elementary  gases  leads  to  similar 
conclusions  in  regard  to  their  molecules.  The  molecule 
of  a  few  elementary  gases  has  been  shown  to  consist  of 
4  atoms,  that  of  some  of  3  atoms,*  and  that  of  a  few  others 
of  a  single  atom;  but  usually  the  condition  is  that  found  in 
hydrogen  and  chlorine.  The  view  is  thus  forced  upon  IKS 
that  the  molecules  of  elementary  gases  consist  of  atoms  of 
the  same  kind,  just  as  the  molecules  of  compound  gases 
consist  of  atoms  of  different  kinds.  The  molecule  of 
hydrogen  is  a  compound  of  two  atoms  of  hydrogen,  just  as 
the  molecule  of  hydrochloric  acid  is  a  compound  of  an  atom 
of  hydrogen  and  an  atom  of  chlorine.  According  to  this 
conception,  when  hydrogen  gas  and  chlorine  gas  are 
brought  together,  the  complete  action  is  not  represented 
by  the  equation 

II  -f  Cl  =  HC1. 

/ 

*  In  speaking  of  ozone,  it  was  stated  that  when  oxygen  is  changed 
to  ozone  there  is  a  diminution  of  volume  from  three  to  two  without 
change  of  weight.  In  other  words,  the  specific  gravity  of  oxygen 
is  two  thirds  that  of  ozone.  But  the  specific  gravity  of  oxygen  leads 
to  the  conclusion  that  its  molecule  contains  two  atoms.  Similarly, 
the  specific  gravity  of  ozone  leads  to  the  conclusion  that  its  molecule 
contains  three  atoms.  Ozone  is  therefore  believed  to  be  made  up 
of  molecules  each  of  which  consists  of  three  atoms  of  oxygen  ;  and 
ordinary  oxygen  to  be  made  up  of  molecules  each  of  which  consists 
of  two  atoms  of  oxygen.  The  molecular  weight  of  ordinary  oxygen 
is  32,  and  that  of  ozone  is  48. 


2 TO  INTRODUCTION   TO   CHEMISTRY. 

The  molecules  of  hydrogen  and  chlorine  must  be  broken 
up  before  the  act  of  combination  can  take  place.  Hence, 
there  are  two  acts  involved  in  passing  from  hydrogen  gas 
and  chlorine  gas  to  hydrochloric  acid.  These  are  : 

HH     -j-     C1C1     =     II  +  H  +  Cl 

Molecule  of        Molecule  of  Atoms  of 

hydrogen.  chlorine.  hydrogen. 

Then,    further,    the    atoms    combine    to    form    compound 
molecules : 

H  -f  II  +  Cl  +  01  =  2HC1. 

Or  we  may  write  the  equation  thus : 

H2         +         C12  2HC1. 

Molecule  of  Molecule  of 

hydrogen.  chlorine. 

The  process  of  dissociation  similar  to  ionizatiou  in  solu- 
tions probably  plays  an  important  part  in  the  combination 
of  gaseous  substances. 

Again,  when  an  elementary  gas  such  as  hydrogen  or 
oxygen  is  set  free  from  a  compound,  it  appears  from  the 
above  that,  at  the  instant  it  is  liberated,  it  exists  in  the 
atomic  condition,  but  that  if  there  is  nothing  else  present 
with  which  the  atoms  can  combine,  they  combine  with  each 
other  to  form  molecules.  After  it  has  been  set  free,  there- 
fore, it  should  be  less  active  than  at  the  instant  it  id  set 
free.  This  is  quite  in  accordance  with  many  curious  and 
well-known  facts. 

Nascent  State. — It  is  found  that  at  the  instant  elements 
are  set  free  from  their  compounds  they  are  capable  of 
effecting  changes  which  they  cannot  effect  after  they  have 
once  been  set  |ree.  Thus,  free  oxygen  gas  passed  into 
hydrochloric  acid  produces  no  change  under  ordinary  con- 
ditions; but  oxyge.n  liberated  from  a  compound  in  contact 
with  hydrochloric  acid  decomposes  the  latter  and  sets 


RELATIONSHIP   OF  PHYSICS  AND  CHEMISTRY.      211 

chlorine  free.  Hydrogen  gas  passed  into  nitric  acid  causes 
no  change;  but  hydrogen  liberated  in  direct  contact  with 
nitric  acid  reduces  the  acid  to  ammonia  in  some  cases. 
Many  other  examples  of  this  kind  of  action  might  be  cited. 
The  simplest  explanation  of  the  phenomenon  is  that  offered 
above.  An  element  at  the  instant  of  its  liberation  is  said 
to  be  in  the  nascent  state. 

Relation  of  Physics  and  Chemistry  to  Molecules. — Ac- 
cording to  what  has  been  said,  all  substances,  elementary 
as  well  as  combined,  are  made  up  of  molecules.  The 
molecules  are  believed  to  have  the  properties  of  the  sub- 
stance as  we  know  it  in  the  free  state.  The  molecule  is 
<the  smallest  particle  of  a  substance  that  can  exist  in  the 
free  state.  The  molecules  are  said  to  be  held  together  by 
cohesion.,  and,  theoretically,  a  substance  could  be  separated 
into  its  molecules  by  purely  mechanical  processes.  As  long 
as  action  upon  a  substance  does  not  involve  decomposition 
of  the  molecules,  the  action  is  in  the  realm  of  physics. 
The  molecules  are  made  up  of  atoms.  The  atom  enters 
into  chemical  action  and  is  the  largest  particle  of  a  sub- 
stance that  can  do  so.  Chemistry  is  that  science  which 
has  to  deal  with  changes  within  the  molecules.  It  must 
be  remembered  that  these  statements  are  not  statements  of 
facts  known  to  us.  The  laws  of  definite  and  multiple  pro- 
portions are  statements  of  facts  as  far  as  these  are  known ; 
but  when  we  come  to  speak  of  atoms  and  molecules  we  are 
dealing  with  conceptions  which,  however  probable  they 
may  appear,  can  nevertheless  not  be  proved  to  be  true. 
\Vc  make  use  of  these  conceptions  because  they  simplify 
our  dealings  with  the  facts  of  chemistry,  and  suggest  lines 
of  inquiry  which  lead  to  discoveries  of  value. 

Explanation  of  the  Laws  Governing  the  Combination  of 

Gases.— It  has  been  pointed  out  (pages  150-153)  that  when 
hydrogen  combines  with  chlorine,  with,  oxygen,  and  with 


212  INTRODUCTION    TO   CHEMISTRY. 

nitrogen  the  relations  between  the  volumes  of  the  combin- 
ing gases  are  simple,  and  that  these  volumes  in  turn  bear 
a  simple  relation  to  the  volumes  of  the  products  formed. 
The  explanation  of  these  facts  on  the  basis  of  Avogadro's 
hypothesis  is  as  follows: 

In  equal  volumes  of  hydrogen  and  of  chlorine  there  is 
the  same  number  of  molecules.  Each  molecule  of  hy- 
drogen and  each  molecule  of  chlorine  consists  of  two 
atoms.  When  hydrogen  and  chlorine  combine,  one  atom 
of  one  combines  with  one  of  the  other,  so  that  from  one 
molecule  of  hydrogen  and  one  of  chlorine  two  molecules 
of  hydrochloric-acid  gas  are  formed.  The  number  of 
molecules  is  the  same  after  combination  as  before,  and 
therefore  the  product  occupies  the  same  volume  as  the 
uncombiiied  gases.  When  hydrogen  combines  with 
oxygen,  however,  two  atoms  of  hydrogen  combine  with 
one  of  oxygen.  The  reaction  is  represented  thus: 

2H2  +  02  =  2H20. 

In  this  case  two  molecules  of  hydrogen  and  one  molecule 
of  oxygen  give  two  molecules  of  water,  and  the  volume  of 
the  product  in  the  form  of  vapor  is  only  two  thirds  that  of 
the  combining  gases.  The  reaction  between  nitrogen  and 
hydrogen  is  represented  thus  : 


3H 


Or,  from  four  molecules  only  two  are  obtained.  Conse- 
quently the  volume  of  the  product  is  only  half  that  of  the 
uncombined  gases. 

How  a  Formula  is  Determined.  —  Chemical  formulas 
were  first  introduced  for  the  purpose  of  expressing  the 
composition  of  substances.  They  might  be  used  for  this 
purpose  at  present  without  having  any  connection  whatever 


HOW  A  FORMULA  IS  DETERMINED.  213 

with  the  conception  of  atoms  and  molecules,  but  the  diffi- 
culty would  then  be  to  decide  upon  the  combining  weights 
of  the  elements.  It  would  be  possible  for  authoritative 
bodies  to  unite  in  issuing  an  edict  that  the  combining 
weights  of  the  elements  shall  be  certain  figures  which  are 
in  harmony  with  facts  known.  But  this  would  hardly  be 
a  scientific  mode  of  procedure ;  and  there  might  exist 
differences  of  opinion  in  regard  to  the  advisability  of 
accepting  the  figures.  When,  however,  we  once  accept 
the  atomic  theory  and  the  hypothesis  of  Avogadro,  we  have 
a  definite  basis  to  work  on,  and  there  is  little  opportunity 
for  disagreement  in  regard  to  the  figures  to  be  adopted. 

The  necessary  steps  in  the  determination  of  the  formula 
of  a  compound  may  be  illustrated  by  the  case  of  water. 
The  compound  is  first  analyzed  and  found  to  contain 
hydrogen  and  oxygen  in  the  proportion  of  1  part  hydrogen 
to  8  parts  oxygen.  This  is  a  fact.  But  we  wish  to  express 
by  our  formula  not  only  the  composition  of  the  substance, 
but  the  composition  of  a  molecule  of  the  substance. 
We  therefore  determine  the  molecular  weight  by  the 
method  described  above  by  comparing  the  specific  gravity 
of  its  vapor  with  that  of  hydrochloric  acid  or  hydrogen. 
We  find  that  the  molecular  weight  is  18.  In  other  words, 
the  molecule  of  water,  or  the  smallest  particle  of  water,  is 
18  times  heavier  than  an  atom  of  hydrogen.  According 
to  the  analysis,  the  18  parts  are  made  up  of  2  parts  of 
hydrogen  and  16  parts  of  oxygen.  By  an  examination  of 
a  large  number  of  gaseous  compounds  containing  oxygen 
we  conclude  that  16  is  the  atomic  weight  of  oxygen,  as  the 
smallest  weight  of  oxygen  found  in  any  of  its  compounds 
is  16  times  heavier  than  the  smallest  weight  of  hydrogen 
found  in  any  of  its  compounds.  Therefore,  the  molecule 
of  water  consists  of  2  atoms  of  hydrogen  and  1  atom  of 
oxygen.  The  formula  representing  the  facts  and  concep- 
tions in  regard  to  the  composition  of  water  is  H20. 


214  INTRODUCTION   TO   CHEMISTRY. 

Raoult's  Laws. — Studies  of  solutions  have  shown  that 
the  following  laws  hold  good: 

1.  When  weights  of  substances  that  are  proportional  to 
their  molecular  weights  are  dissolved  in  the  same  volume  of 
a  solvent,  the  same  rise  of  the  lolling -point  is  caused  in  each 
case. 

2.  When  weights  of  substances  that  are  proportional  to 
their  molecular  weights  are  dissolved  in  the  same  volume  of 
a  solvent,  the  same  lowering  of  the  freezing-point  is  caused 
in  each  case. 

Apparent  Exceptions. — These  laws  have  been  thoroughly 
tested  and  have  been  found  to  hold  good  in  a  large  number 
of  cases.  In  other  cases,  however,  they  do  not  at  first 
sight  appear  to  hold  good.  This  is  notably  the  case  with 
acids,  bases,  and  salts  in  solution  in  water.  In  other 
words,  the  electrolytes  are  exceptions.  The  explanation  is 
believed  to  be  this,  that  these  substances  are  dissociated  by 
water  into  ions,  and  each  ion  acts  like  a  molecule  so  far  as 
its  effect  upon  the  boiling-point  and  the  freezing-point  of 
the  solution  is  concerned.  When  a  molecule  of  sodium 
chloride  of  the  formula  NaCl  is  dissolved  in  water  it  is 
broken  down  into  the  two  ions  Na  and  01,  each  of  which 
produces  the  effect  of  a  molecule  upon  the  boiling-point 
and  upon  the  freezing-point  of  the  solution.  It  was  to 
explain  these  apparent  exceptions  that  the  theory  of  elec- 
trolytic dissociation  (see  page  120)  was  suggested. 

Determination  of  Molecular  Weights  by  the  Boiling- 
point  and  the  Freezing-point  Methods. — If  Raoult's  laws 
are  true,  it  is  plain  that  the  molecular  weights  can  be 
determined  of  substances  that  are  not  dissociated  by  a 
solvent.  The  details  need  not  be  given  here.  Suffice  it 
to  say  that  the  methods  are  based  upon  observations  on  the 
boiling-points  and  the  freezing-points  of  solutions. 


V4LENCE.  215 

Valence.  —  The  formulas  of  the  compounds  thus  far 
studied  have  all  been  determined  by  exactly  the  same 
methods.  On  comparing  the  formulas  of  the  hydrogen 
compounds  of  chlorine,  oxygen,  nitrogen,  and  carbon,  one 
cannot  fail  to  be  struck  by  certain  curious  differences 
between  them.  The  formulas  are 


C1H,     OH2,     NH3,     CH,. 

Speaking  in  terms  of  the  theory,  the  molecule  of  hydro- 
chloric acid  consists  of  1  atom  of  chlorine  combined  with 
1  atom  of  hydrogen;  the  molecule  of  water  consists  of 
1  atom  of  oxygen  combined  with  2  atoms  of  hydrogen;  the 
molecule  of  ammonia  consists  of  1  atom  of  nitrogen  com- 
bined with  3  atoms  of  hydrogen;  the  molecule  of  marsh- 
gas  consists  of  1  atom  of  carbon  combined  with  4  atoms 
of  hydrogen.  It  will  thus  be  seen  that  the  atoms  of 
chlorine,  oxygen,  nitrogen,  and  carbon  differ  in  their 
power  of  holding  hydrogen  in  combination.  The  oxygen 
atom  has  twice  the  power  of  the  chlorine  atom,  the  nitrogen 
atom  has  three  times  this  power,  and  the  carbon  atom  has 
four  times  this  power.  An  examination  of  the  compounds 
of  other  elements  shows  that  other  atoms  differ  from  one 
another  in  the  same  way. 

The  smallest  power,  as  far  as  the  number  of  other  atoms 
which  it  can  hold  in  combination  is  concerned,  is  that  of 
the  chlorine  atom.  And  as  one  chlorine  atom  can  hold 
but  one  atom  of  hydrogen  in  combination,  so  one  atom  of 
hydrogen  can  hold  but  one  atom  of  chlorine  in  combina- 
tion. Either  the  hydrogen  atom  or  the  chlorine  atora 
may  be  taken  as  an  example  of  the  simplest  kind  of  atom. 
An  element  like  hydrogen  and  chlorine  is  called  a  univalent 
element;  an  element  like  oxygen  whose  atom  can  hold  two 
unit  atoms  in  combination  is  called  a  bivalent  element;  an 
element  like  nitrogen  whose  atom  can  hold  three  unit 
atoms  in  combination  is  called  a  trivalent  element;  an 


216  INTRODUCTION    TO   CHEMISTRY. 

element  like  carbon  whose  atom  can  hold  four  unit  atoms 
in  combination  is  called  a  quadrivalent  element.  Most  ele- 
ments belong  to  one  or  the  other  of  these  '  four  classes, 
though  there  are  some  which  can  hold  five,  six,  and  even 
seven  unit  atoms  in  combination.  These  are,  however, 
rare,  and  for  our  present  purpose  they  will  require  but 
slight  notice. 

Valence  is  that  property  of  an  element  by  virtue  of 
which  its  atom  can  hold  a  definite  number  of  other  atoms 
in  combination. 

[Calcium  forms  with  chlorine  the  compound  CaCl2. 
What  is  the  valence  of  calcium  ?  Potassium  and  sodium 
form  chlorides  of  the  formulas  KC1  and  NaCl  respectively. 
What  is  the  valence  of  these  elements  ?  Sulphur  forms 
with  hydrogen  a  compound  of  the  formula  SH2.  What  is 
the  valence  of  sulphur  ?] 

Substituting  Power  of  Elements. — It  has  been  shown  that, 
in  the  formation  of  salts,  metallic  atoms  are  substituted 
for  the  hydrogen  of  acids.  In  such  cases  one  atom  of  a 
univalent  metal  takes  the  place  of  one  atom  of  hydrogen,  one 
atom  of  a  bivalent  metal  takes  the  place  of  two  atoms  of 
hydrogen,  etc.  Thus,  potassium  and  sodium  are  uni- 
valent. An  atom  of  either  takes  the  place  of  one  atom  of 
hydrogen  in  forming  salts.  In  the  formation  of  potassium 
nitrate  from  nitric  acid,  HN03 ,  one  atom  of  potassium  is 
substituted  for  the  one  atom  of  hydrogen  in  the  molecule 
of  nitric  acid,  forming  the  salt  KN03.  So,  also,  in 
sodium  nitrate,  NaN03,  one  atom  of  the  univalent  ele- 
ment sodium  is  substituted  for  one  atom  of  hydrogen. 
In  the  molecule  of  sulphuric  acid,  H2S04 ,  there  are  two 
atoms  of  hydrogen.  To  replace  these,  two  atoms  of  a 
univalent  element  are  required.  Thus,  potassium  sul- 
phate is  K2S04,  and  sodium  sulphate  is  Na2S04.  Ex- 
amples of  salts  containing  bivalent  metals  are  the  follow- 


VARIATIONS  IN   VALENCE.  217 

ing:  Zinc  sulphate,  ZnS04,  in  which  one  atom  of  the 
bivalent  element  zinc  is  substituted  for  the  two  atoms  of 
hydrogen  in  sulphuric  acid;  and  barium  sulphate,  BaS04, 
in  which  one  atom  of  bivalent  barium  takes  the  place  of 
the  two  atoms  of  hydrogen  in  sulphuric  acid. 

When  a  bivalent  metal  forms  a  salt  with  an  acid  like 
nitric  acid,  which  contains  but  one  atom  of  hydrogen  in 
the  molecule,  it  is  believed  that  one  atom  of  the  metal  acts 
upon  two  molecules  of  the  acid,  thus  : 


or 

Cu  +  2HN03  =  Cu(N03)2  +  H2. 

The  formula  of  zinc  nitrate  is  similar,  viz..,  Zn(N03)2. 
In  the  case  of  trivalent  elements  the  matter  is  a  little  more 
complicated,  but  still  simple  enough  if  it  is  borne  in  mind 
that  a  univalent  atom  takes  the  place  of  one  atom  of 
hydrogen  ;  a  bivalent  atom  takes  the  place  of  two  atoms 
of  hydrogen;  a  trivalent  atom  takes  the  place  of  three 
atoms  of  hydrogen,  etc. 

Variations  in  Valence.  —  The  subject  of  valence  is  a  diffi- 
cult one  to  deal  with,  for  the  reason  that  the  valence  of 
an  element  is  not  fixed,  but  varies  according  to  conditions. 
It  may  vary  (1)  according  to  the  temperature.  In  general, 
the  higher  the  temperature  the  lower  the  valence.  Thus, 
phosphorus,  which  is  quinquivalent  towards  chlorine  at 
ordinary  temperatures,  as  is  shown  by  the  formation  of  the 
compound  PC15  ,  is  trivalent  towards  the  same  element  at 
higher  temperatures,  as  is  shown  by  the  fact  that  when 
heated  the  compound  PC15  gives  off  chlorine  and  becomes 
PCI,. 

The  valence  of  the  element  may  vary  (2)  according  to 
the  chemical  character  of  the  element  with  which  it  com- 


218  INTRODUCTION   TO   CHEMISTRY. 

bines.  Thus,  sulphur,  which  is  sexivalent  towards  fluorine 
as  shown  by  the  compound  8F6 ,  is  bivalent  towards 
hydrogen  as  shown  by  hydrogen  sulphide,  SH2;  and 
phosphorus,  which  is  quinquivalent  towards  chlorine  at 
ordinary  temperatures,  is  trivalent  towards  hydrogen,  as 
is  shown  by  the  compound  PH3. 

Generally  speaking,  however,  each  element  shows  a 
tendency  to  act  with  a  particular  valence ;  or  if  it  varies 
at  all,  the  variation  is  between  narrow  limits.  Nitrogen 
appears  as  trivalent  and  quinquivalent ;  carbon  as  bivalent 
and  quadrivalent,  etc. 

Summary. — Avogadro's  hypothesis  that  equal  volumes 
of  all  gases  under  the  same  conditions  of  temperature  and 
pressure  contain  the  same  number  of  molecules  was  sug- 
gested by  a  comparison  of  the  weights  of  equal  volumes  of 
gases,  or  their  specific  gravities,  with  the  combining 
weights  as  found  by  analysis.  The  molecular  weights  of 
substances  bear  to  one  another  the  same  relations  as  the 
specific  gravities  of  their  gases  or  vapors.  Owing  to  a 
peculiarity  of  gases  and  vapors  which  we  cannot  discuss 
here,  their  specific  gravities  are  not  exactly  proportional 
to  their  molecular  weights.  They  are  very  nearly  so. 
From  the  specific  gravity  the  molecular  weight  is  cal- 
culated, and  then  by  analyzing  the  compounds  the  molec 
ular  weight  is  determined  exactly. 

After  analyzing  the  compounds  of  an  element  and 
determining  their  molecular  weights,  the  smallest  quantity 
of  the  element  that  occurs  in  any  of  the  compounds  is 
taken  as  the  atom,  and  the  weight  of  this  quantity  as  com- 
pared with  the  weight  of  the  smallest  quantity  of  hydrogen 
found  in  any  of  its  compounds  taken  as  unity  is  the  atomic 
weight  of  the  element. 

Elementary  gases  and  vapors  are  made  up  of  molecules, 
which  in  turn  consist  of  atoms  of  the  same  kind.  Ele- 


SUMMARY.  219 

ments  are  more  active  in  the  nascent  state  than  in  the  free 
state,  probably  because  the  instant  they  are  set  free  the 
atoms  are  uncombined,  while  after  they  have  been  set  .free 
these  atoms  are  combined  in  the  form  of  molecules. 

Formulas  of  compounds  are  intended  to  represent  the 
composition  of  molecules  and  their  relative  weights. 
Raoult's  laws  concerning  the  relations  between  the  weights 
of  dissolved  substances  and  the  boiling-points  and  freezing- 
points  of  their  solutions  furnish  a  basis  for  the  determina- 
tion of  the  molecular  weights  of  the  substances  in  solution. 

The  valence  of  an  element  is  the  property  by  virtue  of 
which  its  atom  has  the  power  of  holding  in  combination 
a  certain  number  of  other  atoms.  Elements  are  called 
uniyalent,  bivalent,  trivalent,  quadrivalent,  etc.,  accord- 
ing as  they  exhibit  the  simplest  valence  like  that  of 
hydrogen  and  chlorine,  or  double,  treble,  or  quadruple 
this  valence. 

The  substituting  power  of  the  elements  is  determined 
by  the  valence.  An  atom  of  a  univalent  element  can  take 
the  place  of  one  atom  of  hydrogen;  an  atom  of  a  bivalent 
element  can  take  the  place  of  two  atoms  of  hydrogen. 


CHAPTER   XIV. 

CLASSIFICATION    OF   THE    ELEMENTS.— PERIODIC 
LAW. 

General. — It  is  difficult  to  classify  the  elements  satisfac- 
torily, for  the  reason  that,  if  one  set  of  properties  is  made 
the  basis  of  classification,  it  is  questionable  whether  there 
may  not  be  more  fundamental  properties  which  should 
furnish  the  basis.  As  our  knowledge  in  regard  to  the 
fundamental  properties  of  the  elements  increases,  the 
problem  of  classification  will  become  simpler. 

Acid  and  Basic  Properties. — The  chemical  properties 
that  force  themselves  upon  the  attention  most  prominently 
in  every  field  of  chemistry  are  those  which  are  known  as 
acid  properties  and  basic  properties.  As  has  already  been 
pointed  out,  these  two  kinds  of  properties  are  complemen- 
tary. Whatever  developments  there  may  be  in  the  study 
of  chemistry  in  the  future,  it  is  certain  that  the  distinc- 
tion between  these  two  kinds  of  properties  will  always  be 
recognized  as  important.  In  general,  both  acids  and  bases 
contain  oxygen  and  hydrogen.  There  are  some  elements 
whose  compounds  with  hydrogen  and  oxygen  have  basic 
properties,  and  others  whose  compounds  with  hydrogen  and 
oxygen  have  acid  properties.  This  important  fact  may  be 
used  as  the  foundation  of  a  partial  classification  of  the 
elements.  According  to  this,  we  have  (1)  acid-forming 
elements  and  (2)  base-forming  elements.  As  examples  of 
the  first  class,  the  elements  chlorine,  nitrogen,  and  carbon, 
already  studied,  may  be  mentioned.  Examples  of  the 

220 


NATURAL   FAMILIES  OF   THE  ELEMENTS.  221 

second  class  are  sodium,  calcium,  magnesium,  copper, 
iron,  zinc,  etc.  The  last-mentioned  elements  are  generally 
called  metals,  and  the  acid-forming  elements  are  generally 
called  non-metals.  The  line  between  acid-forming  and 
base-forming  elements  cannot  be  drawn  sharply,  for  there 
are  some  elements  that  form  both  acids  and  bases,  accord- 
ing to  the  relative  quantity  of  oxygen  with  which  they  are 
combined.  Thus,  antimony  forms  acids  with  well-marked 
properties,  and  also  other  compounds  which  neutralize 
acids,  and  are  therefore  bases.  The  same  is  true  of 
chromium,  manganese,  and  some  other  elements.  On  the 
other  hand,  there  are  several  elements  that  form  only 
t  acids,  and  several  that  form  only  bases;  and,  further, 
those  which  form  both  acids  and  bases  generally  show  a 
tendency  in  one  direction.  In  dealing  with  the  elements, 
then,  these  differences  in  properties  will  be  taken  into 
account. 

Natural  Families  of  the  Elements. — Another  important 
fact  soon  recognized  is  that  the  elements  fall  into  families 
according  to  their  general  chemical  properties,  the  mem- 
bers of  the  same  family  showing  striking  resemblances  to 
one  another.  Thus,  there  is  the  chlorine  family,  which 
includes,  besides  chlorine  itself,  bromine,  iodine,  and 
fluorine.  It  will  soon  be  seen  that  these  three  elements 
resemble  chlorine  very  closely  indeed,  so  that  what  has 
already  been  learned  in  regard  to  chlorine  will  be  of  great 
assistance  in  the  study  of  the  other  members  of  the  family. 
Further,  there  is  the  sulphur  family,  consisting  of  the 
closely  related  elements  sulphur,  selenium,  and  tel- 
lurium; the  potassium  family,  consisting  of  lithium, 
sodium,  potassium,  rubidium,  and  caesium;  the  calcium 
family,  consisting  of  calcium,  barium,  strontium;  and 
others.  In  all  these  cases  the  resemblance  between  the 
members  of  the  same  family  is  striking. 


222  INTRODUCTION    TO   CHEMISTRY. 

Relations  between  Atomic  Weights  of  the  Elements  and 
their  Properties. — It  has  long  been  known  that  in  many 
cases  there  is  a  connection  between  the  atomic  weights  of 
the  elements  and  their  properties.  This  is  illustrated  by 
the  natural  families  of  which  chlorine,  sulphur,  sodium, 
and  calcium  are  the  best-known  members.  The  members 
of  the  chlorine  family  most  closely  related  to  it  are 
bromine  and  iodine;  those  of  the  sulphur  family  are 
selenium  and  tellurium.  Similarly,  sodium  and  lithium 
are  related  to  potassium ;  and  barium  and  strontium  to 
calcium.  The  atomic  weights  of  these  elements  are  given 
in  the  table  below : 


Chlorine  35.45 
Bromine  79.96 
Iodine..  126.85 


Sulplmr..     32.06 
Selenium.     79.1 
Tellurium  127 


Lithium..  7.03 
Sodium...  23.05 
Potassium  39.15 


Calcium.  .     40 
Strontium    87.6 
Barium...  137.4 


It  will  be  seen  that  the  atomic  weight  of  bromine  is  nearly 
the  mean  of  those  of  the  other  two  members  of  the  family. 

For,   —  -  -  i  --  -  —  =  81.15.     The  same  relation  holds 
« 

in  the  other  families  : 


32.06  +  m=  7.03  +  3905  = 

A  6 

and 

40+137.4 


Similar  relations  are  met  with  throughout  the  list  of 
chemical  elements,  and  a  thorough  study  of  the  subject 
has  led  to  the  remarkable  conclusion  that  the  connection 
between  the  atomic  weights  and  properties  of  the  elements 
is  general.  This  was  first  shown  by  the  Russian  chemist 
Mendeleeff,  the  German  chemist  Lothar  Meyer,  and  the 
English  chemist  Newlands. 

The   Periodic   Law.  —  If,    leaving    out    hydrogen   and 
helium,  and  beginning  with  lithium,  which  next  to  these 


THE  PERIODIC  LAW.  223 

has  the  lowest  atomic  weight,  the  elements  are  arranged 
in  the  order  of  their  atomic  weights,  the  first  fourteen 
exhibit  a  remarkable  relation,  as  shown  in  this  table : 

Li  =    7.08  ;          Gl  =    9.1  ;          B  =  11  ;          C  =  12  ; 
Na  =  23.05 ;        Mg  =  24.36  ;      Al  =  27.1  ;      Si  =  28.4  ; 
X  =  14.04;  0  =  16;  F  =  19  ; 

P  =  31  ;  S  =  32.06  ;          Cl  =  35.45. 

The  elements  whose  symbols  stand  in  the  same  vertical 
column  in  this  table  have  similar  chemical  properties. 
The  resemblance  is  marked  in  the  case  of  lithium  and 
sodium;  carbon  and  silicon;  nitrogen  and  phosphorus; 
oxygen  and  sulphur;  and  fluorine  and  chlorine.  Pro- 
ceeding in  the  same  way,  the  element  with  the  next  higher 
atomic  weight  is  potassium,  39.15.  This  comes  in  the 
same  vertical  column  with  lithium  and  sodium  or  with 
members  of  the  same  family.  Then  follow  calcium, 
scandium,  titanium,  vanadium,  chromium,  and  man- 
ganese, each  of  which  falls  naturally  in  the  vertical  column 
containing  elements  allied  to  it.  It  has  been  found  possi- 
ble in  this  way  to  arrange  all  the  elements  except  hydrogen 
—which,  strange  to  say,  finds  no  place  in  the  system — in 
one  table  exhibiting  the  relations  between  their  atomic 
weights  and  properties.  Several  tables  have  been  pro- 
posed, but  they  do  not  differ  essentially  from  one  another. 
The  table  on  page  224  is  a  simple  arrangement. 

When  the  eighth  element  in  the  order  of  the  inci  easing 
atomic  weights  is  reached  it  is  found  that  it  is  very  much 
like  lithium.  It  is  sodium.  If  this  is  placed  below 
lithium,  and  the  next  six  elements  are  placed  in  the  same 
horizontal  line,  when  the  fifteenth  element  is  reached  it  is 
found  like  the  eighth  to  resemble  lithium.  Up  to  and 
including  manganese  there  are  twenty-one  elements  ex- 
cluding hydrogen.  These  fall  naturally  into  three  series 
of  seven  members  each,  and  arranging  the  symbols  of  these 
horizontally,  those  elements  that  fall  in  the  same  vertical 


224 


INTRODUCTION    TO   CHEMISTRY. 


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THE  PERIODIC  LA IV.  225 

columns  have  the  same  general  character.  The  three 
elements  following  manganese,  viz. ,  iron,  cobalt,  and 
nickel,  are  very  much  alike,  and  they  do  not  belong  in 
any  one  of  the  main  groups.  The  next  element,  copper, 
has  some  properties  which  ally  it  to  the  members  of 
Group  I.  The  next  six  elements  fall  in  Groups  II  to 
VII  and  are  in  their  proper  places,  and  the  next  six  fall 
in  Groups  I  to  VII,  and  are  also  in  their  proper  places  as 
far  as  the  properties  are  concerned.  After  molybdenum 
in  the  sixth  series  comes  a  blank.  There  is  no  element 
known  to  fill  that  place.  It  is,  however,  probable  that 
there  is  one  undiscovered,  with  the  atomic  weight  approxi- 
mately 100  and  with  properties  similar  to  those  of  man- 
ganese. Then  follow  three  elements  which  resemble  one 
another  as  closely  as  iron,  cobalt,  and  nickel.  These  do 
not  belong  in  Groups  I,  II,  and  III,  but  form  a  small 
independent  group.  These  two  groups  of  three  elements 
occur  at  the  end  of  the  fourth  and  sixth  series  respectively. 
One  would  therefore  naturally  expect  a  similar  group  at 
the  end  of  the  eighth  series.  No  such  group  is  known, 
however,  though  at  the  end  of  the  tenth  series,  where  one 
would  naturally  look  for  the  next  similar  small  group, 
there  are  the  three  elements  osmium,  iridium,  and 
platinum.  The  elements  of  Series  2,  beginning  with 
lithium  and  ending  with  fluorine,  differ  in  some  respects 
.  quite  markedly  from  the  other  elements  of  the  groups  to 
which  they  belong,  as  will  be  seen  later.  Beginning  with 
sodium,  it  will  be  seen  that  there  are  two  series  of  seven 
elements  and  a  short  series  of  three ;  then  again  two  series 
of  seven  and  a  series  of  three;  and,  although  the  following 
series  are  imperfect,  it  is  easy  to  recognize  that  the  same 
general  arrangement  of  the  elements  holds  good  to  the 
end.  A  series  of  seven  elements  is  called  a  short  period; 
while  two  short  periods  with  the  accompanying  three 
similar  elements  constitute  a  long  period.  The  remarkable 


226  INTRODUCTION   TO   CHEMISTRY, 

relations  thus  presented  are  summed  up  in  the  periodic 
law : 

The  properties  of  an  element  are  periodic  functions  of  its 
atomic  weight. 

Composition  of  Compounds  with  Hydrogen  and  with 
Oxygen. — Passing  from  left  to  right  in  each  series,  the 
elements  combine  with  a  larger  and  larger  relative  quantity 
of  oxygen.  The  only  oxygen  compound  of  lithium  has 
the  formula  Li20.  The  oxide  of  glucinum  is  G10;  that  of 
boron,  B203;  the  highest  oxide  of  carbon  is  C02;  that  of 
nitrogen,  N205:  that  of  sulphur,  S03;  and  that  of  chlorine, 
C1207.  On  the  other  hand,  the  power  to  combine  with 
hydrogen  increases  from  right  to  left  until  a  limit  is 
reached,  as  is  shown  by  the  formulas  FH,  OH2,  NH3, 
and  CH4. 

Acid-forming  and  Base-forming  Elements. — Those  ele- 
ments which  have  the  strongest  metallic  character,  whose 
hydroxides  are  the  strongest  bases,  are  included  in 
Group  I.  The  hydroxides  of  the  metals  in  Group  II  are 
weaker  bases,  those  of  the  elements  in  Group  III  are  weaker 
still,  while  the  hydroxides  of  some  of  the  elements  included 
in  Group  IV  have  weak  acid  properties  and  no  basic 
properties.  The  elements  of  Group  V  are  nearly  all  acid- 
forming.  Those  of  Group  VI  form  strong  acids,  as  do 
those  of  Group  VII. 

The  Weight  of  its  Atom  Determines  the  Properties  of 
an  Element. — If  the  atomic  weight  of  an  element  is  known, 
its  position  in  the  table  is  known,  and  from  its  position  its 
properties  can  be  stated  with  considerable  accuracy. 
When  the  table  was  first  constructed,  the  three  elements 
scandium,  gallium,  and  germanium  were  undiscovered. 
It  was  seen,  however,  that  the  gaps  existed,  and  it  was 
predicted  that  elements  would  be  found  with  atomic 


PLAN   TO  BE  FOLLOWED.  227 

weights  approximately  44,  69,  and  72  respectively,  and 
that  these  elements  would  have  certain  properties  which 
were  clearly  described.  It  was  suggested  that  the  element 
with  the  atomic  weight  44  would  bear  to  calcium  and 
titanium  about  the  same  relation  that  aluminium  bears  to 
magnesium  and  silicon.  The  predictions  were  soon  after- 
ward confirmed,  and  the  description  of  the  element  given 
before  it  was  discovered  was  found  to  be  singularly  correct. 
The  predictions  in  regard  to  gallium  and  germanium  were 
also  verified  most  strikingly.  Unquestionably  the  proper- 
ties of  the  elements  are  determined  by  their  atomic 
weights.  An  element  whose  atom  weighs  100  times  as 
much  as  that  of  hydrogen  must  have  certain  definite 
properties.  It  must  combine  with  hydrogen  and  with 
oxygen  in  certain  proportions;  it  must  be  allied  to  the 
members  of  the  chlorine  family;  its  properties  are  the 
result  of  that  particular  weight.  Further,  it  seems  to 
follow  that  the  elements  are  not  entirely  independent 
forms  of  matter,  but  that  they  are  in  all  probability  com- 
pounds of  a  small  number  of  simple  elements  at  present 
unknown  to  us.  Of  this,  however,  there  is  no  evidence, 
and  until  some  one  succeeds  in  isolating  one  or  more  of 
these  subtler  elements  it  is  almost  useless  to  speculate  in 
regard  to  them. 

Plan  to  be  Followed. — The  elements  hydrogen,  oxygen, 
chlorine,  nitrogen,  and  carbon  have  been  studied  in  order 
to  illustrate  the  methods  of  studying  chemical  problems 
in  general,  and  as  examples  of  the  chemical  elements. 
Now,  following  the  suggestions  of  the  periodic  law,  a 
number  of  other  elements  will  be  treated  as  members  of 
families  or  groups.  Hydrogen  does  not  belong  to  any 
group.  Oxygen  has  peculiarities  that  distinguish  it  from 
most  other  elements,  but  it  nevertheless  resembles  sulphur 
in  many  ways,  and  the  two  are  treated  together.  Chlorine, 


228  INTRODUCTION    TO   CHEMISTRY. 

as  already  stated,  belongs  to  a  group  of  which  fluorine, 
bromine,  and  iodine  are  the  other  members.  Nitrogen 
belongs  to  a  group  of  which  phosphorus,  arsenic,  and 
antimony  are  the  other  best-known  members.  Carbon 
also  belongs  to  a  group,  silicon  being  the  other  well-known 
member.  We  therefore  have  the  following  groups  first  to 
deal  with: 

CHLORINE  GROUP.      SULPHUR  GROUP.      NITROGEN  GROUP.      CARBON  GROUP. 
Chlorine,  Sulphur,  Nitrogen,  Carbon, 

Bromine,  Selenium,  Phosphorus,  Silicon. 

Iodine,  Tellurium.  Arsenic, 

Fluorine.  Antimony. 

Bismuth. 

The  principal  members  of  these  groups  are  acid-forming 
elements.  They  are  generally  called  non-metals.  In  the 
nitrogen  group,  however,  two  of  the  members  are  both 
acid-forming  and  base-forming.  There  is  a  gradation  in 
the  properties  from  nitrogen  to  bismuth. 

As  the  object  of  this  book  is  to  present  concisely  such 
facts  as  serve  to  illustrate  the  general  character  of  chem- 
ical action  and  the  general  principles  of  the  science  of 
chemistry,  it  will  not  be  necessary  to  go  into  details  in 
dealing  with  these  groups.  One  member  of  each  group 
having  been  studied  comparatively  fully,  the  other  mem- 
bers may  be  treated  briefly.  It  will  thus  be  possible  to  get 
a  clearer  idea  of  the  principles  of  the  science  than  by 
attempting  to  study  a  large  number  of  facts  the  connection 
between  which  can  be  but  dimly  discerned,  if  discerned  at 
all. 

After  the  acid-forming  elements  have  been  studied,  the 
base-forming  elements  will  be  taken  up  in  a  similar  way; 
but,  as  will  be  seen,  the  chemistry  of  the  acid-forming 
elements  exhibits  more  variety,  and  is  hence  better  adapted 
to  the  illustration  of  the  general  principles  of  the  science 
than  that  of  the  base-forming  elements,  so  that  the  latter 
need  not  be  treated  as  fully. 


CHAPTER   XV. 

THE   CHLORINE   GROUP: 
CHLORINE,    BROMINE,    IODINE,    FLUORINE. 

THE  three  members  of  this  group  which  show  the  most 
marked  resemblance  are  chlorine,  bromine,  and  iodine. 
Fluorine  has  properties  of  the  same  general  kind,  and  its 
compounds  resemble  those  of  the  other  three  members  of 
the  group,  so  that  it  is  properly  treated  with  them. 

Bromine,  Br  (At.  Wt.  79.96).  —  This  element  occurs  in 
nature  in  company  with  chlorine.  Chlorine,  as  has  been 
stated,  occurs  mostly  in  combination  with  sodium,  as 
sodium  chloride,  or  common  salt.  In  several  of  the  great 
salt-beds  there  is  some  bromine  in  the  form  of  sodium 
bromide,  NaBr,  and  in  some  places  it  occurs  as  potassium 
bromide,  KBr. 

Preparation.  —  The  process  of  preparation  of  bromine  in 
the  laboratory  is  the  same  as  that  made  use  of  for  prepar- 
ing chlorine.  It  will  be  remembered  that  in  order  to  get 
chlorine  from  sodium  chloride  the  salt  is  first  converted 
into  hydrochloric  acid,  and  this  is  then  oxidized.  So,  too, 
in  order  to  get  bromine  from  sodium  bromide,  it  may  first 
be  converted  into  hydrobromic  acid,  and  this  then  oxi- 
dized. The  reactions  involved  are  usually  : 


-  H2S04  =  N^S04  +  2HBr; 
2HBr  -f  0  =  H20  +  2Br, 

229 


23°  INTRODUCTION    TO   CHEMISTRY. 

As  in  the  case  of  chlorine,  the  substance  commonly  used 
is  manganese  dioxide,  when  the  reaction  takes  place 
according  to  the  following  equation  : 

4HBr  +  Mn02  =  MnBr,  f  211,0  +  2Br. 

[Kei'er  back  to  the  explanation  of  this  reaction  given 
under  the  head  of  Chlorine.  What  other  methods  might 
be  used  in  the  preparation  of  bromine  ?] 

On  the  large  scale  bromine  is  made  by  treating  mag- 
nesium bromide  with  chlorine  : 


Properties.—  -Bromine  is  a  heavy,  dark  red  liquid  at 
ordinary  temperatures.  It  is  easily  converted  into  vapor 
which  is  brownish  red.  At  —  7.3°  it  is  solid.  It  has  an 
extremely  disagreeable  smell,  to  which  fact  it  owes  its 
name  (from  /JpoS/Yo?,  a  stench). 

Its  properties  are,  in  general,  like  those  of  chlorine.  It 
acts  violently  upon  organic  substances.  It  attacks  the 
skin  and  the  membranes  lining  the  passages  of  the  throat 
and  lungs  in  much  the  same  way  as  chlorine.  Wounds 
caused  by  the  liquid  coming  in  contact  with  the  skin  are 
painful  and  serious.  It  must  be  handled  with  great  care. 
With  water  at  low  temperatures  it  forms  a  hydrate  corre- 
sponding to  chlorine  hydrate,  of  the  formula  Br2.10H20, 
which  decomposes  when  left  in  contact  with  the  air  at 
ordinary  temperatures.  It  dissolves  slightly  in  water, 
forming  a  colored  solution  called  bromine-water. 

Its  chemical  conduct  is  also  like  that  of  chlorine.  It 
combines  with  many  elements  directly  and  with  great 
avidity.  Its  combination  with  arsenic  and  some  other 
elements  is  accompanied  by  an  evolution  of  light  and  heat, 
as  in  the  case  of  chlorine.  Its  compounds  with  other 
elements  are  called  bromides.  While  acting  in  general  in 
the  same  way  as  chlorine,  it  is  a  somewhat  weaker  element, 


HYDROBROMIC  ACID.  231 

so  that  chlorine  drives  it  out  of  its  compounds  and  sets  it 
free. 

EXPERIMENT  102. — Mix  together  3.5  grams  potassium  bromide 
and  7  grams  manganese  dioxide.  Put  the  mixture  into  a  500-cc. 
flask  ;  connect  with  a  condenser  (see  Fig.  25).  Mix  15  cc.  con- 
centrated sulphuric  acid  and  90  cc.  in  water.  After  the  liquid  is 
cool  pour  it  upon  the  mixture  in  the  flask.  Heat  gently,  when 
bromine  will  be  given  off  in  the  form  of  vapor.  Apart  of  this  will 
condense  and  collect  in  the  receiver.  Perform  this  experiment 
under  a  hood  with  a  good  draught.  In  treating  the  manganese 
dioxide  and  potassium  bromide  together  with  sulphuric  acid,  the 
action  takes  place  as  represented  in  the  following  equation  : 

2KBr  +  MnO2  +  2H2SO4  =  K»S04  +  MnSO4  +  2H2O  +  Bra. 

Hence  both  potassium  sulphate,  K2SO4,  and  manganese  sulphate, 
MnSO4 ,  are  left  behind  in  the  flask. 

[When  sulphuric  acid  acts  upon  manganese  dioxide  at  high  tem- 
perature the  action  takes  place  thus  : 

MnO2  +  H2SO4  =  MnSO4  +  H2O  +  O. 

If  this  action  took  place  in  the  presence  of  hydrobromic  acid, 
what  effect  would  the  liberated  oxygen  have  ?  Suppose  the  oxygen 
were  allowed  to  escape  from  the  flask  containing  the  manganese 
dioxide  and  sulphuric  acid,  and  then  passed  into  hydrobromic 
acid,  would  the  same  result  be  reached  as  when  the  hydrobromic 
acid  is  in  the  flask  from  which  the  oxygen  is  liberated  ?  What 
is  the  commonly  accepted  explanation  ?  If  the  formula  of  man- 
ganese sulphate  is  MnSO4 ,  what  is  the  valence  of  manganese  ? 
What  would  you  expect  the  formula  of  manganese  chloride  to  be? 
Of  manganese  oxide?  Is  the  valence  of  manganese  greater 
toward  oxygen  or  toward  chlorine  ?] 

Hydrobromic  Acid,  HBr. — The  only  compound  that 
bromine  forms  with  hydrogen  alone  is  hydrobromic  acid. 
This  is  in  all  respects  very  much  like  hydrochloric  acid. 
It  is  made  in  the  same  way.  It  is  a  colorless  gas  that 
fumes  in  the  air  in  consequence  of  its  attraction  for 
moisture.  Its  solution  in  water  acts  very  much  like 
ordinary  hydrochloric  acid.  The  elements  are  not  held 


232  INTRODUCTION   TO   CHEMISTRY. 

together  as  firmly  iu  hydrobromie  as  in  hydrochloric  acid. 
This  is  shown  by  its  decomposition  under  circumstances 
in  which  hydrochloric  acid  is  stable.  Thus,  for  example, 
it  is  decomposed  by  sulphuric  acid,  while  hydrochloric  acid 
is  not.  The  hydrogen  is  separated  from  the  bromine  and 
acts  upon  the  sulphuric  acid,  while  the  bromine  is  given 
off  as  such.  Hence,  when  potassium  bromide  is  treated 
with  sulphuric  acid,  hydrobromie  acid  is  given  off,  together 
with  bromine  and  a  compound  of  sulphur  and  oxygen 
which  is  formed  by  the,  action  of  hydrogen  on  the  sulphuric 
acid. 

EXPERIMENT  103. — In  a  small  porcelain  evaporating-dish  put  a 
few  crystals  of  potassium  bromide.  Pour  upon  them  a  few  drops 
of  concentrated  sulphuric  acid.  The  white  fumes  of  hydrobromie 
acid  and  the  reddish-brown  vapor  of  bromine  are  noticed.  Treat 
a  few  crystals  of  potassium  or  sodium  chloride  in  the  same  way. 
What  difference  is  there  between  the  two  cases  ? 

Compounds  with  Hydrogen  and  Oxygen. — With  hy- 
drogen and  oxygen  bromine  forms  compounds  that  resem- 
ble very  closely  those  which  chlorine  forms  with  the  same 
elements.  The  principal  ones  are  bromic  and  hypobromous 
acids.  The- potassium  salt  of  bromic  acid,  HBr03,  is 
formed  by  treating  a  strong  solution  of  caustic  potash  with 
bromine : 

3Br,  +  6KOH  =  oKBr  +  KBrO,  +  3H80. 

The  potassium  salt  of  hypobromous  acid,  HBrO,  is 
formed  by  treating  a  dilute  solution  of  caustic  potash  with 
bromine : 

Br2  +  2KOH  =  KBr  +  KBrO  +  H20. 

Iodine,  1  (At.  Wt.  126.85).— This  element  occurs  in 
nature  in  combination  with  sodium,  in  company  with 
chlorine  and  bromine,  but  in  smaller  quantity  than  either. 
It  is  also  found  in  larger  quantities  in  all  sea-plants.  It 


PROPERTIES   OF  IODINE.  233 

is  obtained  largely  from  the  latter  source.  On  the  coast 
of  Scotland  and  France  the  sea-weed  which  is  thrown  up 
by  storms  is  gathered,  dried,  and  burned.  The  organic 
portions  are  thus  destroyed  [What  is  the  meaning  of  the 
word  destroyed  used  in  this  sense  ?]  and  the  mineral  or 
earthy  portions  are  left  behind  as  ashes.  This  incom- 
bustible residue,  which  is  called  kelp,  contains  sodium 
iodide.  Sea-weed  is  also  cultivated  for  the  sake  of  the 
sodium  iodide  contained  in  it.  Chili  saltpetre,  or  the 
sodium  nitrate  found  in  Chili,  contains  some  sodium- 
iodide,  and  this  now  furnishes  a  considerable  quantity  of 
the  iodine  of  commerce. 

Iodine  is  obtained  from  sodium  iodide,  just  as  chlorine 
and  bromine  are  obtained  from  their  compounds  with 
sodium  and  potassium.  [Give  the  equations  representing 
the  steps  which  must  be  taken  in  order  to  separate  iodine 
from  sodium  iodide.] 

EXPERIMENT  104.— Mix  together  about  2  grams  of  sodium  or 
potassium  iodide  and  4  grams  manganese  dioxide.  Treat  with  a 
little  sulohuric  acid  in  a  one  to  two  litre  flask.  Heat  gently  on  a 
sand-bath.  Gradually  the  vessel  will  be  filled  with  the  beautiful 
colored  vapor  of  iodine.  In  the  upper  parts  of  the  flask  some  of 
the  iodine  will  be  deposited  in  the  form  of  crystals  of  a  grayish- 
black  color. 

Properties. — At  ordinary  temperatures  iodine  is  a  gray- 
ish-black crystallized  solid.  It  is  volatile  at  ordinary  tem- 
peratures. It  acts  upon  the  mucous  membranes,  though 
less  energetically  than  chlorine  and  bromine.  It  colors 
the  skin  yellowish-  brown,  and  acts  as  an  absorbent,  caus- 
ing the  reduction \of  swellings.  It  melts  at  113-115°,  and 
boils  at  250°,  when  it  is  converted  into  a  violet  vapor. 

The  action  of  iodine  is,  in  general,  the  same  as  that  of 
chlorine  and  bromine,  only  its  action  is  weaker.  Hydro- 
bromic  acid,  as  we  have  seen,  is  a  weaker  compound  than 
hydrochloric  acid.  Hydriodic  acid  is  still  weaker.  Chlo- 


234  INTRODUCTION    TO   CHEMISTRY. 

rine   acting   upon   hydrobromic   acid   sets  bromine    free. 
Chlorine  and  bromine  set  iodine  free  from  hydriodic  acid. 
Iodine  dissolves  slightly  in  water,  easily  in  alcohol,  and 
easily  in  a  water-solution  of  potassium  iodide. 

EXPERIMENT  105. — Make  solutions  of  iodine  in  water,  in  alco- 
hol, and  in  a  water-solution  of  potassium  iodide.  Use  small 
quantities  in  test-tubes. 

When  a  solution  containing  free  iodine  is  treated  with  a 
little  starch-paste,  the  solution  turns  blue,  in  consequence 
of  the  formation  of  a  complex  compound  of  starch  and 
iodine.  Bromine  and  chlorine  do  not  form  blue  com- 
pounds. Advantage  is  taken  of  this  fact  to  distinguish 
iodine  from  the  other  members  of  the  same  family. 

EXPERIMENT  106. — Make  some  starch-paste  by  covering  a  few 
grains  of  starch  in  a  porcelain  evaporating-dish  with  cold  water, 
grinding  this  to  a  paste,  and  pouring  200-300  cc.  boiling-hot 
water  on  it.  After  cooling  add  a  little  of  this  paste  to  a  dilute 
water-solution  of  potassium  iodide  to  which  has  been  added  a  very 
little  iodine.  The  solution  will  turn  blue  if  the  conditions  are 
right.  Now  add  a  little  of  the  paste  to  a  dilute  water-solution  of 
potassium  iodide.  There  is  no  change  of  color,  because  the  iodine 
is  in  combination  with  the  potassium.  Add  a  drop  or  two  of  a 
solution  of  chlorine  in  water,  when  the  blue  color  will  appear. 
The  explanation  of  this  phenomenon  is  that  the  chlorine  sets  the 
iodine  free,  and  the  free  iodine  then  acts  upon  the  starch,  pro- 
ducing the  blue  compound.  [How  can  you  show  that  the  chlo- 
rine itself  will  not  form  a  blue  compound  with  starch  ?] 

Hydriodic  Acid,  HI,  is  analogous  to  hydrochloric  and 
hydrobromic  acids.  It  is  set  free  from  its  compounds  by 
treating  them  with  sulphuric  acid,  but  it  is  even  more  un- 
stable than  hydrobromic  acid,  and  hence  breaks  down  into 
hydrogen  and  iodine.  The  iodine  is  liberated,  while  the 
hydrogen  acts  on  the  sulphuric  acid,  as  it  does  in  the  case 
of  hydrobromic  acid. 

EXPERIMENT  107. — Treat  a  few  crystals  of  potassium  iodide 
with  sulphuric  acid.  [What  do  you  notice?]  Compare  the  result 


JODIC  ACID. -FLUORINE.— HYDROFLUORIC  ACID.     235 

with  that  obtained  in  the  case  of  potassium  bromide  and  sodium 
chloride. 

lodic  Acid,  HI03. — The  principal  compound  of  iodine 
with  hydrogen  and  oxygen  is  iodic  acid,  HI03,  which 
corresponds  to  chloric  and  bromic  acids.  It  is  known 
principally  in  the  form  of  its  potassium  salt,  potassium 
iodate,  KI03.  When  heated,  this  salt,  like  the  chlorate 
and  the  bromate,  gives  up  all  its  oxygen,  potassium  iodide, 
KI,  being  left  behind. 

Fluorine,  F  (At.  Wt.  19). — This  element  occurs  in 
nature  in  large  quantity,  and  widely  distributed,  but  always 
in  combination  with  other  elements.  It  is  found  chiefly 
in  combination  with  calcium,  as  fluor-spar,  or  calcium 
fluoride^  CaF2,  and  in  combination  with  sodium  and 
aluminium,  as  cryolite,  a  mineral  which  occurs  abundantly 
in  Greenland  and  has  the  composition  3NaF.AlFs,  being 
a  complex  compound  of  sodium  fluoride  and  aluminium 
fluoride. 

All  attempts  to  obtain  fluorine  in  the  free  state  failed 
until  a  few  years  ago,  when  its  isolation  was*  effected  by 
passing  an  electric  current  through  liquid  hydrofluoric 
acid  containing  potassium  fluoride  in  solution  in  a  vessel 
of  platinum-indium. 

Properties. — Fluorine  is  the  most  active  of  all  the 
elements  at  ordinary  temperatures.  It  is  a  greenish- 
yellow  gas.  It  acts  upon  almost  all  substances.  Thus,  it 
decomposes  water,  yielding  ozone  and  hydrofluoric  acid; 
afc  ordinary  temperatures  it  combines  directly  with  sul- 
phur, phosphorus,  iron,  etc.,  with  evolution  of  light  and 
heat.  It  does  not,  however,  act  upon  platinum. 

Hydrofluoric  ax;id,  I  IF,  is  made  from  fluor-spar  by  treat- 
ing it  with  sulphuric  acid.  The  action  is  of  the  same 


236  INTRODUCTION   TO  CHEMISTRY. 

kind  as  that  which  takes  place  when  hydrochloric  acid  is 
liberated  from  sodium  chloride  : 

CaF2  -f  H2S04  =  CaS04  +  2HF. 

It  is  a  colorless  gas,  with  strong  acid  properties.  It 
greatly  irritates  the  membranes  lining  the  respiratory 
organs,  and  hence  care  should  be  taken  not  to  inhale  it.  It 
acts  upon  glass,  dissolving  it,  and  must  therefore  be  kept 
in  vessels  of  rubber,  lead,  or  platinum,  upon  which  it  does 
not  act.  Its  action  on  glass  consists  in  the  transformation 
of  silicon  dioxide,  or  silica,  Si02  ,  which  is  contained  in  all 
kinds  of  glass,  into  silicon  tctrafluoride,  SiF4  ,  which  is  a 
gas.  The  action  is  represented  thus  : 


Si02  +  4HF  =  SiF4  +  2H20. 

EXPERIMENT  108.  —  In  a  lead  or  platinum  vessel  put  a  few  grams 
(5-6)  of  powdered  fluor-spar  and  pour  upon  it  enough  concentrated 
sulphuric  acid  to  make  a  thick  paste.  Cover  the  surface  of  a 
piece  of  glass  with  a  thin  layer  of  wax  or  paraffin,  and  through 
this  scratch  some  letters  or  figures,  so  as  to  leave  the  glass  ex- 
posed where  the  scratches  are  made.  Put  the  glass  over  the  ves- 
sel containing  the  fluor-spar,  and  let  it  stand  for  some  hours. 
Take  off  the  glass,  scrape  off  the  coating,  and  the  figures  which 
were  marked  through  the  wax  or  paraffin  will  be  found  etched  on 
the  glass. 

The  acid  is  used  for  etching  glass,  particularly  for 
marking  scales  on  thermometers,  barometers,  and  other 
graduated  glass  instruments.  A  solution  of  the  gas  in 
water  is  manufactured  for  this  purpose  and  kept  in  rubber 
bottles.  '. 

Fluorine  does  not  combine  with  oxygen.  This  is  also 
true  of  helium  and  argon. 

Comparison  of  the  Members  of  the  Chlorine  Group.  —  In 
considering,  first,  the  physical  properties  of  these  ele- 
ments, we  notice  that  all,  with  the  exception  of  fluorine, 
form  colored  gases  or  vaporsT—  At  ordinarytemperatureS 


MEMBERS   OF   THE  CHLORINE  GROUP  COMPARED.    237 

chlorine  is  a  £as,  bromine  a  liquid,  and  iodine  a  solid.  In 
regard  to  their^hemical  conduct,  it  may  be  said  that,  in 
general,  fluorine  is  the  most  energetic;  chlorine  comes 
next  in  order,  then  bromine,  and  lastly  iodine.  This  is 
seen  particularly  in  the  relative  stability  of  their  com- 
pounds with  hydrogen.  Their  compounds  with  metals 
also  show  the  same  relation.  On  the  other  hand,  with 
oxygen  the  order  is  reversed.  Fluorine  does  not  unite  with 
oxygen  at  all.  The  compounds  of  chlorine "an^  oxygen 
are  very  unstable;  those  with  bromine  rather  more  stable; 
and  one  compound  of  iodine  and  oxygen  is  comparatively 
stable. 

The  elements  of  this  group  combine  with  hydrogen  and 
with  other  elements  in  the  simplest  way.  They  are  all 
univalent. 

The  compounds  formed  by  th$  three  elements  chlorine, 
bromine,  and  iodine  with  hydrogen  and  oxygen  have 
analogous  composition,  and  are  formed  by  analogous 
reactions.  Thus,  we  have  the  hydrogen  compounds: 

HC1,     HBr,     and     HI; 

and  the  compounds  with  hydrogen  and  oxygen  : 

HC10         HBrO  

HC10., 

HCIO"         HBrOs         HIO, 


HC10,         HIO 


The  properties  of  any  compound  of  one  element  are 
similar  to  those  of  the  compounds  of  analogous  composi- 
tion of  the  other  elements  of  the  group. 

All  these  facts  seem  to  indicate  that  these  elements  are 
not  distinct  forms  of  matter  entirely  independent  of  one 
another,  but  rather  that  they  contain  some  common  con- 
stituent. The  relations  between  the  atomic  weights  of  the 
members  of  the  group  have  already  been  referred  to. 


CHAPTER   XVI. 

THE   SULPHUR   GROUP: 
SULPHUR,    SELENIUM,   TELLURIUM. 

Sulphur,  S  (At.  Wt.  32.06).— The  principal  member  of 
this  group  is  sulphur.  In  nature  it  is  frequently  found 
accompanied  by  small  quantities  of  selenium,  and  some- 
times by  tellurium.  It  has  been  known  in  the  elementary 
form  from  the  earliest  times,  for  the  reason  that  it  occurs 
abundantly  in  this  form  in  nature.  It  is  found  particu- 
larly in  the  neighborhood  of  volcanoes,  as  in  Sicily,  which 
is  the  chief  source  of  the  sulphur  of  commerce.  It  occurs, 
further,  in  combination  with  many  metals  as  sulphides,— 
as  in  iron  pyrites,  FeS2;  copper  pyrites,  FeCuS2;  galenite, 
PbS,  etc. ;  in  combination  with  metals  and  oxygen  as  sul- 
phates— for  example,  as  calcium  sulphate,  or  gypsum, 
CaS04  +  2H20;  barium  sulphate,  or  heavy  spar,  BaS04; 
lead  sulphate,  PbS04;  in  a  few  vegetable  and  animal 
products  in  combination  with  carbon,  hydrogen,  and, 
generally,  with  nitrogen. 

Extraction  of  Sulphur  from  its  Ores. — When  taken  from 
the  mines,  sulphur  is  mixed  with  earthy  substances  from 
which  it  must  be  separated.  This  separation  is  accom- 
plished by  piling  the  ore  in  such  a  way  as  to  leave  passages 
for  air.  The  piles  are  covered  with  material  to  prevent 
free  access  of  air,  and  the  mass  is  then  lighted  below.  A 
part  of  the  sulphur  burns,  and  the  heat  thus  furnished 
melts  the  rest  of  the  sulphur.  The  molten  sulphur  runs'1 

238 


SULPHUR.  239 

down  to  the  bottom  of  the  pile,  and  is  drawn  off  from  time 
to  time.  If  the  pile  were  not  protected  from  free  access 
of  air,  the  sulphur  would  burn  up,  yielding  a  gas,  sulphur 
dioxide,  S02. 

[What  analogy  is  there  between  this  process  and  that 
employed  in  making  charcoal  ?  What  are  the  essential 
differences  between  the  two  processes  ?] 

Refining  of  Sulphur. — The  crude  brimstone  thus  obtained 
is  afterwards  refined  by  distillation,  and  it  is  this  distilled 
sulphur  which  comes  to  market  under  the  names  "roll 
brimstone  "  and  *  *  flowers  of  sulphur. "  The  distillation 
is  carried  on  in  earthenware  retorts  connected  with  large 
chambers  of  brick-work.  When  the  vapor  of  sulphur  first 
comes  into  the  condensing-chamber  it  is  suddenly  cooled, 
and  hence  deposited  in  the  form  of  a  fine  powder.  This 
is  called  "flowers  of  sulphur."  After  the  distillation  has 
continued  for  some  time,  the  vapor  condenses  in  the 
form  of  a  liquid,  which  collects  at  the  bottom  of  the 
chamber.  This  is  drawn  off  into  wooden  moulds  and  takes 
the  form  of  "roll  brimstone"  or  "stick  sulphur/' 

Properties, — Sulphur  is  a  yellow,  brittle  substance  which 
at  —  50°  is  almost  colorless.  It  melts  at  114.5°,  forming 
a  thin,  straw-colored  liquid.  When  heated  to  a  higher 
temperature  it  becomes  darker  and  darker  in  color,  and  at 
200°  to  250°  it  is  so  viscid  that  the  vessel  in  which  it  is 
contained  may  be  turned  upside  down  without  danger  of 
its  running  out.  Finally,  at  448.4°  it  boils  and  is  then 
converted  into  a  brownish-yellow  vapor. 

EXPERIMENT  109.— Distil  about  10  grams  of  roll  sulphur  from 
an  ordinary  glass  retort.  Notice  the  changes  above  described. 
Collect  the  liquid  sulphur  which  passes  over,  in  a  beaker-glass 
containing  cold  water. 

Crystals  of  Sulphur. — When  molten  sulphur  solidifies, 
or  when  it  is  deposited  from  a  solution,  its  particles 


24°  INTRODUCTION   TO   CHEMISTRY. 

arrange  themselves  in  regular  forms  called  crystals.  But, 
strange  to  say,  the  crystals  formed  from  molten  sulphur 
are  entirely  different  from  those  deposited  from  solutions 
of  sulphur.  The  former  are  honey-yellow  needles.  The 
latter  are  octahedrons  with  rhombic  base,  which  is  also 
the  form  of  the  sulphur  found  in  nature.  A  careful 
examination  of  the  needles  shows  that  the  angles  which 
their  faces  form  with  one  another  are  not  the  same  as  the 
angles  formed  by  the  faces  of  the  octahedrons,  and  that 
the  crystals  are  constructed  on  a  different  plan.  The 
needles  belong  to  the  monoclinic  system  of  crystals,  and 
the  octahedrons  to  the  rhombic  system. 

Crystallography. — Notwithstanding  the  infinite  number 
of  forms  assumed  by  solids  in  passing  from  the  liquid  to 
the  solid  state  and  when  deposited  from  solutions,  it  lias 
been  shown  that  all  can  be  referred  to  a  very  few  systems. 
Usually  six  systems  are  adopted.  These  are : 

1.  THE  REGULAR  SYSTEM.     All  the  crystals  belonging 
to  this  system  can  be  referred  to  three  axes  of  equal  length,, 
and  at  right  angles  to  one  another,  crossing  at  the  centre. 
Examples  of   crystals   belonging  to  this  system  are   the 
regular  octahedron  and  tfce  cube.  v  The  three  axes  are  the 
imaginary  lines  which  pass  through  the  solid  angles  of  the 
octahedron.     All  the  other  forms  of  this  system  may  be 
referred  to  this  octahedron-. 

2.  THE  TETRAGONAL  SYSTEM.     In  this  the  forms  are 
referred  to  three  axes  at  right  angles,  two  of  equal  length 
and  one  differing  from  the  other  two.     The  fundamental 
forms  are  the  octahedron  and  prism. 

3.  THE   HEXAGONAL   SYSTEM.      The   crystals   of  this 
system  are  referred  to  four  axes,  —three  of  equal  length 
inclined  at  60°  to  one  another,  and  a  fourth  at  a  right 
angle  to  them,  which  is  either  of  the  same  length  or  of  a 
different  length.     The  six-sided  pyramid  and  prism  are  the 
principal  forms. 


CRYSTALLOGRAPHY.  241 

4.  THE  RHOMBIC  SYSTEM.     The  crystals  belonging  to 
this  system  have  three  axes,  of  unequal  lengths,  at  right 
angles  to  one  another. 

5.  THE   MONOCLINIC    SYSTEM.      In   this   system   the 
crystals  have  three  axes, — two   at  right  angles   to   each 
other,  the  third  at  right  angles  to  one  and  inclined  to  the 
other. 

6.  THE  TRICLIXIC  SYSTEM.     The  crystals  belonging  to 
this  system  are  referred  to  three  axes,  all  inclined  to  one 
another. 

[It  would  be  well  to  have  a  set  of  models  of  the  principal 
forms  of  the  six  systems  of  crystals  available,  and  to  study 
these  until  the  general  principles  of  the  classification  are 
clear.  Examples  of  crystals,  either  such  as  occur  in  nature 
or  such  as  are  made  artificially,  should  also  be  studied,  and 
the  system  to  which  they  belong  determined.] 

The  subject  of  crystallography  is  one  that  cannot  be 
made  clear  in  a  few  words.  It  requires  careful  study  and 
much  practice  in  observing  forms  of  crystals.  Prom  what 
has  just  been  said,  however,  it  will  be  seen  that  the  system 
of  classification  of  crystals  is  a  simple  one.  For  our 
present  purpose,  the  fact  should  be  specially  emphasized 
that  the  crystalline  form  of  a  substance  is  a  definite  prop- 
erty, by  means  of  which  it  may  be  distinguished  from 
other  substances.-  The  fact  that  a  substance  crystallines 
in  the  regular  system  is  just  as  characteristic  of  that  sub- 
stance as  the  fact  that  it  boils  or  melts  at  a  certain  point. 
Thus,  we  know  that  ice  always  melts  at  0°,  and  that  water 
solidifies  at  0°.  We  should  be  much  surprised  to  find 
water  solidifying  at  some  other  temperature,  say  20°. 
Similarly,  knowing  that  sulphur  occurs  in  nature  crystal- 
lized in  forms  which  belong  to  the  rhombic  system,  we  are 
naturally  surprised  to  find  that,  when  molten  sulphur 
solidifies,  it  crystallizes  in  forms  belonging  to  the  mono- 
clinic  system.  What  is  perhaps  still  stranger  is  the  fact 


242  INTRODUCTION    TO   CHEMISTRY. 

that  when  the  honey -yellow  needles  are  allowed  to  stand 
unmolested  they  spontaneously  undergo  a  change.  They 
become  opaque;  their  color  changes;  and  now,  if  examined 
carefully,  they  are  found  to  consist  of  minute  crystals  like 
those  found  in  nature.  It  is  evident  that  the  arrangement 
of  the  particles  in  the  monoclinic  crystals  of  sulphur  is  not 
a  stable  one. 

Substances  that  crystallize  in  two  distinct  forms  are 
called  dimorphous.  Carbon  crystallizes  in  two  different 
forms  [What  are  they?];  and  is  hence  dimorphous. 

EXPERIMENT  110. — In  a  covered  porcelain  crucible  melt  a  few 
grams  of  roll  sulphur.  Let  it  cool  slowly,  arid  when  a  thin  crust 
has  formed  on  the  surface  make  a  hole  through  this  and  pour  out 
the  liquid  part  of  the  sulphur.  The  inside  of  the  crucible  will  be 
found  lined  with  the  honey-yellow  needles  which,  as  has  been 
stated,  belong  to  the  monoclinic  system.  Take  out  a  few  of  the 
crystals  and  examine  them.  Are  they  brittle  or  elastic  ?  What 
is  their  color?  Are  they  opaque,  transparent,  or  translucent? 
Lay  the  crucible  aside,  and  in  the  course  of  a  few  days  again 
examine  the  crystals.  What  changes,  if  any,  have  taken  place  ? 

Other  Forms  of  Sulphur. — Sulphur  can  also  be  obtained 
in  the  amorphous,  or  uncrystallized,  condition.  That 
which  was  collected  under  water  in  Experiment  109  will 
be  found,  to  be  soft  and  doughlikc.  It  is  amorphous. 
After  a  time  it  becomes  brittle.  When  separated  from  a 
compound  which  is  dissolved  in  water,  it  is  finely  divided, 
and  gives  the  liquid  an  appearance  suggesting  milk. 

Crystallization  from  Carbon  Bisulphide. — Sulphur  is  in- 
soluble in  water,  slightly  soluble  in  alcohol  and  ether.  It 
dissolves  in  carbon  bisulphide,  CS2,  and  from  the  solution 
it  is  deposited  in  rhombic  crystals. 

EXPERIMENT  111. — Dissolve  2  to  3  grams  roll  sulphur  in  5  to 
10  cc.  carbon  bisulphide.  Filter  through  a  fluted  filter.  Put  the 
solution  in  a  shallow  vessel,  and  allow  the  carbon  bisulphide  to 


HYDROGEN  SULPHIDE.  243 

evaporate  by  standing  in  the  air.     The  sulphur  will  remain  be- 
hind in  the  form  of  crystals. 

Chemical  Conduct  of  Sulphur. — Sulphur  combines  with 
oxygen  when  heated  to  a  sufficiently  high^temperature, 
forming  sulphur  dioxide,  S02.  [Compare  carbon  mid 
sulphur  in  this  respect.]  It  combines  readily  with  most 
metals,  forming  sulphides,  which  are  analogous  to  the 
oxides.  Its  combination  with  iron  has  already  been  shown 
in  Experiment  10.  It  also  combines  with  copper,  the  act 
being  accompanied  by  light  and  heat. 

EXPERIMENT  112. — In  a  dry  wide  test-tube  heat  some  sulphur  to 
boiling.  Introduce  into  it  small  pieces  of  copper-foil  or  sheet- 
copper.  Or  hold  a  narrow  piece  of  sheet-copper  so  that  the  end 
just  dips  into  the  boiling  sulphur. 

Hydrogen  Sulphide,  Sulphuretted  Hydrogen,  H2S. — 
When  hydrogen  is  passed  over  highly-heated  sulphur,  the 
two  elements  combine  to  form  hydrogen  sulphide.  [Is 
there  any  analogy  between  this  process  and  the  formation 
of  water  by  the  burning  of  hydrogen  ?]  This  compound 
of  sulphur  and  hydrogen  occurs  in  nature  in  solution  in 
the  so-called  sulpmir  waters,  which  are  met  with  in  many 
parts  of  this  and  other  countries.  It  also  issues  from  the 
earth  in  some  places.  It  is  formed  by  heating  organic 
substairnes  that  contain  sulphur,  just  as  water  is  formed 
by  heating  organic  substances  that  contain  oxygen,  and 
ammonia  by  heating  such  as  contain  nitrogen.  It  is 
formed,  further,  by  decomposition  of  organic  substances 
that  contain  sulphur,  as,  for  example,  the  albumin  of  eggs. 
The  odor  of  rotten  eggs  is  partly  due  io  the  formation  of 
lydrogen  sulphide. 

Preparation.— In  the  laboratory  the  gas  is  most  readily 
made  by  treating  a  sulphide  with  an  acid.  When  a  metal, 


244  INTRODUCTION   TO   CHEMISTRY. 

as  iron,  is  treated  with  sulphuric  acid,  hydrogen  is  given 
off  and  the  iron  salt  of  the  acid  is  formed  thus  : 


When  sulphuric  acid  acts  upon  the  oxide  of  iron, 
hydrogen  is  given  off  in  combination  with  oxygen  as 
water,  thus: 

FeO  -{-  H2S04  =  FeS04  +  H20. 

Finally,  when  sulphuric  acid  acts  upon  iron  sulphide, 
hydrogen  is  given  off  in  combination  with  sulphur  as 
hydrogen  sulphide,  thus: 

FeS  +  HSS04  =  FeS04  +  H2S. 

A  similar  explanation  holds  for  other  acids.  For  ex- 
ample, hydrochloric  acid  acts  upon  iron  sulphide  in 
accordance  with  the  equation 

2HC1  +  FeS  =  FeCl2  +  H2S. 

EXPERIMENT  113.  —  Arrange  an  apparatus  as  shown  in  Fig.  51. 
Put  a  small  handful  of  iron  sulphide,  FqS^  in  the  flask,  and  pour 
dilute  hydrochloric  acid  upon  it.  Pass  the  evolved  gas  through 
a  little  water  contained  in  the  wash-cylinder  A.  Pass  some  6f 
the  gas  into  water.  [What  evidence  have  you  that  it  dissolves?] 
Collect  some  by  displacement  of  air.  Its  specific  gravity  is  1.178. 
[Should  the  vessel  be  placed  with  the  mouth  down  or  up  ?]  Set 
fire  to  some  of  the  gas  contained  in  a  cylinder.  If  there  is  free 
access  of  air,  the  sulphur  burns  to  sulphur  dioxide,  and  the 
hydrogen  to  water. 

Properties.  —  Hydrogen  sulphide  is  a  colorless,  trans- 
parent gas  of  specific  gravity  1.178.  It  has  an  extremely 
disagreeable  odor,  somewhat  suggestive  of  that  of  rotten 
eggs.  It  is  poisonous,  even  small  quantities  causing  head- 
ache, vertigo,  nauseaj  and  Bother  bad  symptoms.  It  is 


HYDROGEN  SULPHIDE. 


245 


soluble  in  water,  about  three  volumes  being  taken  up  at 
ordinary  temperatures.  This  solution  is  used  in  the 
laboratory  instead  of  the  gas.  Hydrogen  sulphide  is  easily 
decomposed  into  its  elements.  In  consequence  of  this 
instability,  it  causes  a  number  of  changes  which  the 
analogous  compound  water  cannot  effect.  The  relations 
here  are  similar  to  those  which  exist  between  hydrochloric 


FIG.  61. 

and  hydriodic  acids.  Hydrochloric  acid  is  very  stable, 
while  hydriodic  acid  breaks  down  readily  into  hydrogen 
and  iodine.  Chlorine,  bromine,  and  iodine  act  upon 
hydrogen  sulphide,  setting  the  sulphur  free  and  combining 
with  the  hydrogen.  Thus,  with  chlorine  the  action  takes 
place  as  represented  in  the  equation 

H,S  -f  C12  =  2HC1  -f  S. 

[Does  chlorine  ever  act  in  a  similar  way  on  water? 
Under  what  circumstances  ?  What  is  the  peculiarity  of 
the  oxygen  given  off  ?] 

Most  metals  when  heated  in  the  gas  are  converted  into 


246  INTRODUCTION    TO   CHEMISTRY. 

sulphides.     Thus,  when  it  is  passed  over  heated  iron  this 
reaction  takes  place : 

Fe  +  H2S  =  FeS  +  »,. 

[What  takes  place  when  water-vapor  is  passed  over 
heated  iron  ?] 

Many  of  the  sulphides  are  insoluble  in  water.  Hence, 
when  hydrogen  sulphide  is  passed  through  solutions  con- 
taining metals  in  the  form  of  soluble  salts,  the  insoluble 
sulphides  are  thrown  down,  or  precipitated. 

EXPERIMENT  114. — Pass  hydrogen  sulphide  successively  through 
solutions  containing  a  little  lead  nitrate,  zinc  sulphate,  and 
arsenic  prepared  by  dissolving  a  little  white  arsenic,  or  arsenic 
trioxide,  As2O3 ,  in  dilute  hydrochloric  acid.  In  the  vessel  con- 
taining the  lead  a  black  precipitate  of  lead  sulphide  will  be 
formed  ;  in  the  one  containing  the  zinc  sulphate  there  will  be 
formed  a  white  precipitate  of  zinc  sulphide  ;  in  the  one  contain- 
ing the  arsenic,  a  straw-yellow  precipitate  of  arsenic  sulphide 
will  be  formed.  In  all  these  cases  the  hydrogen  of  the  hydrogen 
sulphide  and  the  metal  of  the  salt  exchange  places.  For  exam- 
ple, in  the  case  of  zinc  sulphate  the  reaction  takes  place  thus  : 

ZnSO*  -I-  HaS  =  ZnS  +  H2SO*. 

Chemical  Analysis.  —  In  dealing  with  chemical  sub- 
stances the  first  thing  we  have  to  determine  is  their  com- 
position, or:  in  other  words,  we  have  to  analyze  them. 
For  this  purpose  the  properties  of  the  elements  and  their 
general  conduct  towards  chemical  substances  must,  of 
course;  be  known.  To  facilitate  the  process  of  analysis 
the  mixture  to  be  examined  is  usually  brought  into  solution 
and  then  treated  successively  with  certain  substances,  the 
effect  being  observed  in  each  case.  Suppose  we  had  ar 
solution  containing  most  of  the  metallic  elements  in  the 
form  of  salts.  If  we  were  to  pass  through  this  solution 
hydrogen  sulphide,  some  of  the  metals  would  be  precipi- 


HYDROSULPHIDES.  247 

tated  in  the  form  of  sulphides,  while  others  would  remain 
in  solution,  as  their  sulphides  are  soluble.  We  then  filter 
off  the  precipitate  and  examine  it  by  other  methods,  and 
we  could  also  further  examine  the  solution  from  which  the 
sulphides  were  precipitated.  By  adding  to  this  another 
reagent  which  will  precipitate  some  of  the  metals  and  leave 
the  others  in  solution,  we  can  learn  still  more  in  regard  to 
the  composition  of  the  substance  under  examination.  Hy- 
drogen sulphide  is  constantly  made  use  of  in  the  laboratory 
for  the  purposes  of  analysis. 

Hydrosulphides. — When  hydrogen  sulphide  acts  upon 
hydroxides,  the  action  consists  in  the  formation  of  hydro- 
sulphides.  In  the  case  of  potassium  hydroxide  the  action 
takes  place  thus: 

KOH  +  H2S  =  KSH  +  H20. 

The  oxygen  and  sulphur  simply  exchange  places. 

If  only  half  enough  hydrogen  sulphide  is  passed  into  the 
solution  to  effect  the  above  change,  a  sulphide  is  formed 
thus: 

2KOH  -f  H2S  =  K2S  +  2H?0. 

Or  if  hydrogen  sulphide  is  allowed  to  act  on  potassium 
sulphide,  the  product  is  potassium  hydrosulphide : 

K2S  +  H2S  =  2KSH. 

Compounds  of  Sulphur  with  Oxygen  and  with  Hydrogen 
and  Oxygen. — When  sulphur  burns  in  the  air  it  forms  the 
dioxide  S02.  Under  certain  conditions  the  dioxide  com- 
bines with  more  oxygen,  forming  the  trioxide  S03.  When 
sulphur  dioxide  acts  upon  water,  sulphurous  acid  is. 
formed : 

S03  +  H30  =  H2S08. 


248  INTRODUCTION    TO   CHEMISTRY. 

[What  analogy  is  there  between  the  acid  thus  formed 
and  carbonic  acid  ?] 

When  the  trioxide  combines  with  water,  sulphuric  acid 
is  formed  : 

S03  +  H20  =  H2S04. 

Sulphur  Dioxide,  S00.  —  This  compound  is  formed  by 
burning  sulphur  in  the  air  or  in  oxygen.  It  issues  from 
volcanoes  in  large  quantities.  It  is  best  prepared  by  treat- 
ing copper  with  sulphuric  acid.  The  action  does-  not  take 
place  without  the  aid  of  heat.  The  copper  appears  first 
to  reduce  the  acid,  forming  sulphurous  acid,  H2S03  ,  and 
copper  oxide,  CuO,  the  former  compound  breaking  down 
at  once,  however,  into  sulphur  dioxide  and  water,  and  the 
latter  dissolving  in  sulphuric  acid  as  sulphate.  These 
changes  are  represented  by  the  three  equations  : 

(1)  H2S04  +  Cu  =  H2S03  +  CuO; 

(2)  H2S03  -  H20  +  S02; 

(3)  H2S04  +  CuO  =  CuS04  -f  H20. 

Or  combined  in  one  equation  these  may  be  represented 
thus: 

2H2S04  +  On  =  CuS04  +  2H20 


[Compare  the  action  of  copper  on  sulphuric  acid  with 
that  of  copper  on  nitric  acid.  What  analogy  is  there 
between  the  two  cases  ?  What  difference  ?] 

Sulphur  dioxide  is  a  colorless  gas  of  an  unpleasant, 
suffocating  odor,  familiar  to  every  one  as  that  of  burning 
sulphur-matches.  Water  absorbs  it  readily.  It  is  easily 
liquefied  by  cold. 

EXPERIMENT  115.  —  Put  eight  or  ten  pieces  of  sheet-copper,  one 
to  two  inches  long  and  about  half  an  inch  wide,  in  a  500-cc. 
flask  ;  pour  15  to  20  cc.  concentrated  sulphuric  acid  upon  it.  On 
heating,  sulphur  dioxide  will  be  evolved.  The  moment  the  gas 


SULPHUROUS   ACID. 


249 


begins  to  come  off,  lower  the  flame,  and  keep  it  at  such  a  height 
that  the  evolution  of  gas  is  regular  and  not  too  active.  Pass 
some  of  the  gas  into  a  bottle  containing 
water.  Fill  a  vessel  by  displacement  of  air. 
Its  specific  gravity  is  2.26.  See  whether  the 
gas  will  burn  or  support  combustion. 

EXPERIMENT  116.—  Arrange  an  apparatus 
as  shown  in  Fig.  52.  A  is  a  funnel-tube 
provided  with  a  stop-cock.  In  the  flask  put 
a  40  per  cent  solution  of  acid  sodium  sulphite, 
HNaSO3  ;  in  the  funnel,  after  closing  the 
stop-cock,  put  ordinary  concentrated  sul- 
phuric acid.  Open  the  stop-cock  very  little, 
so  that  the  sulphuric  acid  drops  into  the 
solution  below.  A  regular  evolution  of  sul- 
phur dioxide  can  thus  be  maintained.  FIG.  52. 

Sulphurous  Acid,  H2S03.  —  The  solution  of  sulphur 
dioxide  in  water  has  acid  properties,  and  probably  contains 
the  ions  of  the  acid  H2S03.  By  neutralizing  the  solution 
with  bases,  the  sulphites,  or  salts  of  sulphurous  acid,  are 
obtained.  The  sulphites  are  analogous  to  the  carbonates 
in  composition,  and  suffer  the  same  decomposition  when 
treated  with  acids.  When  a  carbonate  is  treated  with  an 
acid,  carbon  dioxide  is  given  off.  So,  also,  when  a  sul- 
phite is  treated  with  an  acid,  sulphur  dioxide  is  given  off: 


28          2 
Na2S0.3  +  8HC1 


Na2S04  -f  H20  -f  S02, 
SNadl  +  H20  +  SO,. 


When  a  solution  of  sulphur  dioxide  is  allowed  to  stand 
in  the  air  in  loosely-stoppered  bottles,  it  takes  up  oxygen, 
the  sulphurous  acid  being  converted  into  sulphuric  acid  : 

H2SOS  +  0  =  H2S04. 

Sulphur  dioxide  is  a  good  bleaching  agent,  and  is  ex- 
tensively used  for  the  purpose  of  bleaching  wool,  silk, 


25°  INTRODUCTION   TO   CHEMISTRY. 

straw,  paper,  etc.  In  some  cases  the  bleaching  is  due  to 
the  fact  that  the  sulphur  dioxide  extracts  oxygen  from  the 
colored  substances,  forming  colorless  products.  Tn  other 
cases  the  action  is  more  complicated. 

Sulphur  dioxide  has  the  power  to  check  fermentation, 
and  is  used  to  preserve  liquids  that  have  a  tendency  to 
undergo  fermentation. 

Its  principal  use  is  in  the  manufacture  of  sulphuric 
acid.  For  this  purpose  it  is  made  in  enormous  quantities. 

EXPERIMENT  117. — Burn  a  little  sulphur  in  a  porcelain  crucible 
under  a  bell-jar.  Place  over  the  crucible  on  a  tripod  some 
flowers  or  a  piece  of  calico.  In  the  atmosphere  of  sulphur  dioxide 
these  will  be  bleached.  Or  a  bottle  containing  the  colored  sub- 
stance may  be  filled  with  sulphur  dioxide  and  then  closed. 

Sulphur  Trioxide,  S03. — When  sulphur  dioxide  and 
oxygen  are  passed  together  over  certain  substances  at  a 
somewhat  elevated  temperature  they  unite  to  form  sulphur 
trioxide,  S03.  This  is  a  white  crystallized  solid  that  melts 
at  14.8°  and  boifs  at  46°.  In  contact  with  the  air  it  gives 
off  thick  fumes.  With  water  it  reacts  with  great  energy 
to  form  sulphuric  acid: 

SOS  +  H20  =  H2S04. 

The  substance  best  adapted  to  bringing  about  the  com- 
bination of  sulphur  dioxide  and  oxygen  is  finely-divided 
platinum. 

EXPERIMENT  118.— Prepare  finely  divided  platinum  by  moist- 
ening some  fine  asbestos  with  a  solution  of  platinic  chloride  and 
heating  to  redness  in  a  porcelain  crucible.  The  substance  thus 
obtained  is  called  platinized  asbestos.  Now  arrange  an  appa- 
ratus so  that  both  sulphur  dioxide  and  oxygen  or  air  can  be 
passed  together  through  a  glass  tube,  as  represented  in  Fig.  53. 
First  pass  the  two  gases  dried  by  means  of  calcium  chloride 
through  the  empty  tube  and  heat  a  part  of  the  tube  by  means 
burner.  Is  there  any  evidence  of  combination  ?  Now  stop 


SULPHURIC  ACID.  251 

the  currents  of  the  gases,  let  the  tube  cool  down,  and  introduce 
a  small  layer  of  platinized  asbestos.  Pass  the  dried  gases  over 
the  heated  asbestos.  What  takes  place  ? 

Sulphuric  Acid,  HZS04.  —  Sulphuric  acid  is  found  in 
nature  in  the  form  of  salts,  as  gypsum,  heavy  spar,  etc. 
It  cannot  easily  be  prepared  from  its  salts,  as  nitric  acid 
and  hydrochloric  acids  are,  and  is  generally  made  by  oxi- 


FIG.  53. 

dizing  sulphur  dioxide  in  the  presence  of  water,  or,  in 
other  words,  by  oxidizing  sulphurous  acid*  The  reactions 
involved  in  the  manufacture  of  sulphuric  acid  are: 


H2S03  +  0  =  H2S04. 

Or  sulphur  dioxide  is  oxidized  to  the  trioxide  S08  as  in 
Experiment  118,  and  this  then  treated  with  water,  in 
which  case  the  reactions  are  : 

502  +  0  =  S03; 

503  +  H20  =  H2S04. 

Manufacture  of  Sulphuric  Acid.  —  The  oxidation  of  sul- 
phurous acid  as  represented  in  the  first  series  of  reactions 
above  cannot  readily  be  effected  directly  by  the  action  of 
the  oxygen  of  the  air,  but  an  extremely  interesting  method 
has  been  devised  by  which  the  -oxygen  can  be  transferred 
from  the  air  to  the  sulphurous  acid*.  This  is  accomplished 
by  introducing  sulphur  dioxide  into  largo  chambers 
together  with  compounds  of  nitrogen  and  oxygep,  and 


25  2  INTRODUCTION   TO   CHEMISTRY. 

steam.  The  compound  of  nitrogen  and  oxygen  that  plays 
the  chief  part  in  the  transformation  is  the  trioxide  X2p3. 
The  change  is,  however,  not  one  of  simple  direct  oxidation, 
but  it  involves  a  number  of  reactions.  Nitric  acid  is  used 
as  the  starting-point.  This  at  first  reacts  with  sulphur 
dioxide  and  steam,  as  represented  in  the  equation  : 


H,0.=  2H8SO,  +  N203. 

After  this  the  "main  reactions  are  (I)  the  formation  of  a 

NO 

compound  of  the  formula  S02<^TT2,  called  nitrosyl-sul- 

phuric  acid;  and  (2)  the  decomposition  of  the  nitrosyl- 
sulphuric  acid  by  water.  These  reactions  are  represented 
in  the  two  following  equations  : 

N20S  +  0,  +  H20  =  2S02(OH)(NOZ); 


The  nitrogen  trioxide  formed  in  the  second  reaction 
then  again  enters  into  combination  with  sulphur  dioxide, 
oxygen,  and  water  to  form  nitrosyl-  sulphuric  acid,  which 
again  undergoes  decomposition  with  water.  It  will  be 
seen,  therefore,  that  the  trioxide  is  not  lost,  but  that  it 
serves  the  purpose  of  effecting  the  oxidation  of  the  sul- 
phur dioxide,  and,  theoretically,  a  small  quantity  of  the 
gas  is  capable  of  transforming  an  infinite  quantity  of 
sulphur  dioxide  into  sulphuric  acid. 

Other  reactions  besides  those  mentioned  above  are  un- 
doubtedly involved  in  the  manufacture  of  sulphuric  acid, 
but,  according  to  the  most  elaborate  researches  made  in  a 
factory  in  operation,  those  mentioned  are  the  principal 
ones.  Whatever  the  details  may  be,  the  oxidation  is 
effected  without  difficulty,  and  the  waste  in  nitrogen  com- 
pounds is  now  but  slight. 

In  the  manufacture  of  sulphuric  acid,  sulphur  is  burned 


SULPHURIC  ACID.  253 

and  the  sulphur  dioxide  conducted  into  large  chambers 
lined  with  lead.  The  reason  why  lead  is  used  is  that  sul- 
phuric acid  acts  upon  most  other  available  substances. 

The  above  account  applies  to  the  method  that  has  long 
been  used  in  the  manufacture  of  sulphuric  acid,  and  this 
method  is  still  the  principal  one  in  use.  Recently,  how- 
ever, the  method  illustrated  in  Experiment  118  has  come 
into  extensive  use  especially  for  the  manufacture  of  the 
pure,  concentrated  acid.  Various  substances  are  used,  or 
have  been  recommended,  for  the  purpose  of  effecting  the 
union  of  the  sulphur  dioxide  and  oxygen.  Finely-divided 
platinum  and  ferric  oxide  are  the  principal  ones. 

The  Product, — The  acid  obtained  from  the  leaden  cham- 
bers contains  about  64  per  cent  of  sulphuric  acid.  It  is 
evaporated  in  lead  pans  until  it  reaches  the  specific  gravity 
1.75.  As  stronger  acid  acts  upon  lead,  the  further  evapo- 
ration is  carried  on  in  platinum,  glass,  or  iron.  The 
strong  acid  thus  obtained  is  the  concentrated  sulphuric 
acid  of  commerce,  commonly  called  oil  of  vitriol. 

The  acid  obtained  from  sulphur  trioxide  can,  of  course, 
be  made  of  any  desired  concentration. 

Properties  of  Sulphuric  Acid. — Sulphuric  acid  is  an  oily 
liquid,  usually  somewhat  colored  by  impurities.  The  pure 
acid  is  a  colorless  liquid  at  ordinary  temperatures.  When 
cooled  down  it  forms  crystals.  It  decomposes  the  salts  of 
most  other  acids,  setting  the  acids  free,  and  appropriating 
the  metals."  We  have  already  had  illustrations  of  this 
power  in  the  liberation  of  nitric  and  hydrochloric  acids 
from  their  salts  by  treatment  with  sulphuric  acid. 

[Give  the  equations  representing  the  reaction  that  takes 
place  when  common  salt  and  potassium  nitrate  are  treated 
with  sulphuric  acid.] 

Sulphuric  acid  unites  readily  with  water,  forming  com- 
pounds with  it.  The  simplest  of  these  is  the  hydrate 


*54  INTRODUCTION   TO  CHEMISTRY. 

H2S04  -|-  H20.  This  is  a  crystallized  substance  that  melts 
at  a  low  temperature  (7.5°).  A  great  deal  of  heat  is 
evolved  when  sulphuric  acid  is  mixed  with  water.  This 
fact  has  been  repeatedly  illustrated  in  experiments  already 
performed ;  and  the  necessity  for  precaution  in  mixing  the 
two  liquids  has  been  emphasized.  The  acid  acts  upon 
organic  substances  containing  hydrogen  and  oxygen,  and 
extracts  these  elements  in  the  proportion  to  form  water. 
If  a  piece  of  wood  is  put  in  the  acid  it  is  charred,  in  con- 
sequence of  the  abstraction  of  hydrogen  and  oxygen. 
[How  is  wood  usually  charred  in  the  preparation  of  char- 
coal ?  Is  there  any  analogy  between  the  preparation  of 
charcoal  in  the  ordinary  way  and  by  the  action  of  sulphuric 
acid  ?]  Wounds  caused  by  sulphuric  acid  are  painful  and 
difficult  to  heal.* 

Uses  of  Sulphuric  Acid. — Sulphuric  acid  is  one  of  the 
most  important  chemical  substances.  It  is  used  in 
enormous  quantities  in  the  manufacture  of  sodium  sul- 
phate, of  sodium  carbonate,  of  artificial  fertilizers,  of 
nitroglycerin,  of  glucose,  etc.,  and  in  the  refining  of 
petroleum. 

The  acid  is  used  for  the  purpose  of  drying  gases  upon 
which  it  does  not  act.  [Can  it  be  used  for  drying 
ammonia  ?] 

Monobasic  and  Dibasic  Acids. — Sulphuric  acid  differs 
markedly  from  nitric  and  hydrochloric  acids  in  one 
respect.  It  has  the  power  to  form  two  different  salts  with 
the  same  metal,  in  one  of  which  there  is  twice  as  much 
metal  as  in  the  other.  If  to  a  given  quantity  of  sulphuric 
acid  there  is  added  only  half  the  quantity  of  caustic  potash 
required  to  neutralize  it,  a  salt  is  formed  which  crystallizes. 
It  has  the  composition  represented  by  the  formula  KHS04. 

*  A  paste  made  by  mixing  sodium  carbonate  and  water  should 
quickly  be  applied  to  such  wounds. 


MONOBASIC  AND  Dt A  BASIC  ACIDS.  255 

If  nitric  acid  is  treated  in  the  same  way,  only  half  the  acid 
is  acted  on,  and  the  product  is  potassium  nitrate,  KN03 , 
the  rest  of  the  acid  heing  left  unacted  upon.  In  the  case 
of  sulphuric  acid  two  reactions  are  possible,  viz.: 

H2SO,  +  KOH  =  KHS04  +  H20,     and 
H2S04  +  2KOH  =  K2S04    +  2H20. 

In  the  case  of  nitric  acid  only  one  reaction  seems  to  be 
possible: 

HNO,  +  KOH  B  KN08  +  H20. 

Acids  which,  like  sulphuric  acid,  have  the  power  to 
form  two  salts  with  the  same  univaleiit  metal  are  called 
dibasic  acids.  Acids  which,  like  nitric  acid,  have  the 
power  to  form  only  one  salt  with  the  same  univalent  metal 
are  called  monobasic  acids.  This  power  is  connected  with 
the  number  of  replaceable  hydrogen  atoms  contained  in 
the  molecule  of  the  acids.  An  acid  containing  two  re- 
placeable hydrogen  atoms  in  its  molecule  is  dibasic;  one 
containing  one  replaceable  hydrogen  atom  in  its  molecule 
is  monobasic. 

Acid,  Neutral,  and  Normal  Salts, — A  dibasic  acid  yields 
two  classes  of  salts:  (1)  those  in  which  all  the  hydrogen  is 
replaced,  and  (2)  those  in  which  half  the  hydrogen  is 
replaced  by  metal.  The  former  are  called  normal  salts, 
the  latter  acid  salts.  Normal  salts  are  generally  neutral, 
and  are  sometimes  called  neutral  salts. 

Other  Acids  containing  Sulphur. — Besides  sulphurous 
and  sulphuric  acids,  sulphur  forms  several  other  acids. 
These  cannot  be  treated  of  here.  Their  names  and  for- 
mulas are  as  follows : 

Hyposulphurousacid,  H2S02;  Pyrosulphuric  acid,  H2S20T; 
Thiosulphuric  acid,  H2S20,;     Trithionic  acid,  H2S306; 
Dithionie  acid,  11,8,0.;  Tetrathionic  acid,  H2S,06. 


256  INTRODUCTION   TO   CHEMISTRY. 

The  sodium  salt  of  thiosulphuric  acid,  Na,S20.,,  com- 
monly called  sodium  hyposulphite,  is  used  in  photography. 
Pyrosulphuric  acid,  or  fuming  sulphuric  acid,  breaks  up 
into  sulphuric  acid  and  sulphur  trioxide,  H2S207  =  H2S04 
-f  S03 ,  and  is  a  powerful  reagent  for  some  purposes. 

Carbon  Bisulphide,  CS2. — Sulphur  forms  with  carbon  a 
compound  known  as  carbon  bisulphide,  which  has  the 
composition  represented  by  the  formula  CS2.  It  is  made 
by  bringing  carbon  and  sulphur  together  at  high  tempera- 
tures. It  is  a  liquid  that  boils  at  47°.  That  it  dissolves 
sulphur  has  already  been  seen  (see  Experiments  0  and 
111).  It  also  dissolves  many  other  substances. 

Selenium  and  Tellurium  and  their  Compounds. — These 
elements  are  comparatively  rarely  met  with.  Tellurium 
compounds  are,  to  be  sure,  available  in  large  quantity 
as  a  waste-product  in  the  electrolytic  refining  of  copper. 
In  general,  the  properties  of  the  two  elements  are  very 
similar  to  those  of  sulphur,  and  they  form  compounds 
analogous  to  the  principal  compounds  of  sulphur.  They 
combine  with  hydrogen,  forming  gases  which  have  bad 
odors,  somewhat  resembling  that  of  hydrogen  sulphide. 
They  burn  in  oxygen,  forming  oxides,  Se02  and  Te02. 
Corresponding  to  these  oxides  there  are  acids,  H2Se03 
and  H2Te03,  analogous  to  sulphurous  acid,  and  H2Se04 
and  H2Te04,  analogous  to  sulphuric  acid.  The  com- 
pounds with  hydrogen  are  less  stable  than  hydrogen  sul- 
phide. 

The  relation  between  the  atomic  weights  of  the  three 
elements  of  the  sulphur  group  has  already  been  referred 
to. 

Points  of  Resemblance  between  Oxygen  and  the  Members 
of  the  Sulphur  Group. — Between  the  elements  oxygen  and 
sulphur  there  is  but  little  resemblance,  but  the  compounds 


RESEMBLANCES  BETWEEN   VARIOUS   COMPOUNDS.   257 

of  the  two  elements  present  many  points  of  analogy.  This 
is  seen  particularly  in  the  compounds  which  they  form 
with  hydrogen  and  with  the  metals.  Water  and  hydrogen 
sulphide  are  analogous  in  composition  and  in  their  decom- 
positions. This  is  also  markedly  true  of  the  metallic  oxides 
and  sulphides;  and  of  the  hydroxides  and  hydrosulphides. 
On  the  other  hand,  oxygen  is  unique  in  many  respects, 
and  is  certainly  not  nearly  as  closely  related  to  sulphur  as 
selenium  and  tellurium  are. 


CHAPTER   XVII. 

THE    NITROGEN    GROUP:    NITROGEN,  PHOSPHORUS 
ARSENIC,    ANTIMONY,   AND    BISMUTH. 

General. — Between  the  element  nitrogen  and  the  other 
elements  which  are  included  in  this  group  there  is  but 
little  resemblance.  Nitrogen  is  a  very  inactive  element. 
Phosphorus,  on  the  other  hand,  is  one  of  the  most  active. 
Nitrogen  does  not  combine  directly  with  oxygen.  Phos- 
phorus combines  with  oxygen  even  at  ordinary  tempera- 
tures, while  at  the  burning-temperature  the  combination 
takes  place  energetically.  The  elements  arsenic  and  anti- 
mony resemble  each  other  in  many  respects,  and  are  also 
allied  to  phosphorus;  and  antimony  and  bismuth  resemble 
each  other  closely.  On  studying  the  compounds  which  all 
the  members  of  the  family  form,  the  fact  that  they  are 
closely  related  is  clearly  recognized. 

Phosphorus,  P  (At.  Wt.  31). — This  element  occurs  in 
nature  in  the  form  of  phosphates,  or  salts  of  phosphoric 
acid.  The  chief  of  these  is  calcium  phosphate,  which  is 
the  principal  constituent  of  the  minerals  phosphorite  and 
apatite  and  of  the  ashes  of  bones. 

Preparation. — It  is  prepared  from  bonf-ash.  This  is 
first  treated  with  sulphuric  acid.  The  acid  converts  it 
into  a  compound,  which,  when  mixed  wit  ij  char  coal  and 
heated,  is  reduced,  yielding  free  phosphorus.  The  phos- 
phorus thus  obtained  is  cast  into  sticks  under  water,  and 
preserved  under  water. 

258 


PHOSPHORUS.  259 

Properties. — It  is, colorless  or  slightly  yellow  and  trars- 
lucent.  At  ordinary  temperatures  it  can  be  cut  like  wax, 
but  it  becomes  hard  and  brittle  at  lower  temperatures.  It 
melts  at  a  low  temperature  (44°)  and  boils  at  290°.  Unless 
carefully  protected  from  the  light,  its  appearance  changes. 
It  becomes  opaque  and  darker  in  color,  and  finally  dark 
red.  This  change  can  be  hastened  by  heating  the  phos- 
phorus in  a  sealed  tube  to  a  temperature  of  about  250°. 

It  is  insoluble  in  water,  but  soluble  in  carbon  bisulphide. 
It  is  very  poisonous,  the  inhalation  of  the  vapor  in  small 
quantities  causing  serious  disturbance  of  the  system.  The 
workmen  in  the  factories  in  which  phosphorus  is  made  or 
used  are  frequently  ^affected  by  phosphorus-poisoning. 
Among  the  prominent  symptoms  is  a  gradual  decay  of 
the  bones  (necrosis). 

In  contact  with  the  air  phosphorus  gives  off  fumes  which 
emit  a  pale  light  visible  in  a  dark  room.  It  takes  fire  when 
rubbed  or  cut,  and  must  hence  be  handled  with  great  care. 
It  should  always  be  cut  under  water,  and  never  held  in  the 
hand.  It  not  only  combines  with  oxygen  easily,  but  with 
other  elements,  such  as  chlorine,  bromine,  and  iodine,  the 
action  in  each  case  being  accompanied  by  an  evolution  of 
heat  and  light.  The  combination  of  phosphorus  with 
oxygen  has  already  been  seen.  Its  conduct  towards  iodine 
can  be  shown  by  a  very  simple  experiment. 

EXPERIMENT  119. — Bring  together  in  a  porcelain  crucible  or 
evaporat ing-dish  a  little  phosphorus  and  iodine.  It  will  be  seen 
that  simple  contact  is  sufficient  to  cause  the  two  substances  to 
act  upon  each  other.  Direct  combination  takes  place,  and  the 
action  is  accompanied  by  light  and  heat. 

Red  Phosphorus.— The  red  substance  formed  when  ordi- 
nary phosphorus  is  left  in  the  light,  or  heated  without 
access  of  air,  is  a  second  variety  of  phosphorus  known  as 
red  phosphorus.  This  differs  from  ordinary  phosphorus 


260  INTRODUCTION    TO   CHEMISTRY. 

as  much  as  graphite  differs  from  the  diamond.  Ordinary 
phosphorus  is  very  active,  combining  readily  with  oxygen ; 
it  is  soluble  in  carbon  bisulphide,  and  is  poisonous.  Red 
phosphorus,  on  the  other  hand,  is  inactive.  It  does  not 
change  in  the  air,  and  must  be  heated  to  a  comparatively 
high  temperature  before  it  will  combine  with  oxygen;  it 
is  insoluble  in  carbon  bisulphide,  and  is  not  poisonous. 
Red  phosphorus  is  converted  into  the  ordinary  variety  by 
heating  it  to  about  300°. 

The  cause  of  the  great  difference  in  the  properties  of 
the  two  varieties  of  phosphorus  is  not  known. 

There  are  some  other  modifications  of  phosphorus,  but 
they  are  rarely  met  with. 

Applications  of  Phosphorus. — Phosphorus  is  used  prin- 
cipally in  the  manufacture  of  matches,  and  as  a  poison  for 
vermin.  Various  mixtures  are  used  for  matches.  Xearly 
all  of  them  contain  phosphorus  together  with  some  oxidiz- 
ing compound,  and  some  neutral  substance  to  act  as  a 
medium  for  holding  the  constituents  together.  An  ex- 
ample is  a  mixture  consisting  of  2  parts  phosphorus, 
1  part  manganese  dioxide,  3  parts  chalk,  -J  part  lamp- 
black, and  5  parts  glue.  The  mixture  used  for  "safety- 
matches"  consists  of  potassium  chlorate,  minium,  and 
antimony  trisulphide.  This  will  not  ignite  by  simple  fric- 
tion, but  will  ignite  if  drawn  across  a  paper  on  which  is  a 
mixture  of  red  phosphorus  and  antimony  pentasulphide. 

Phosphine,  Phosphuretted  Hydrogen,  PH3. — The  chief 
compound  of  phosphorus  and  hydrogen  is  phosphine, 
PH3.  It  is  made  by  dissolving  phosphorus  in  caustic 
potash  or  soda.  The  reaction  which  takes  place  is  not 
altogether  simple,  and  need  not  be  explained  at  present. 
The  points  of  chief  interest  in  regard  to  the  substance  are : 
(1)  its  composition,  PH8,  which  is  analogous  to  that  of 


PHOSPH1NE,  PHOSPHURETTED  HYDROGEN.          261 

ammonia,  NH3;  (2)  its  power  to  combine  with  some  acids 
as  ammonia  does,   forming  unstable   phosphonium   salts 
analogous  to  the  ammonium  salts;  and  (3)  its  power  to 
take  fire  when  brought  in  contact  with  the  air. 
It  has  a  disagreeable  odor. 

EXPERIMENT  120. —  Thin  experiment  requires  caution;  a  care- 
less worker  should  not  be  permitted  to  perform  it.  — Arrange  an 
apparatus  as  shown  in  Fig.  54.  In  the  flask  B,  which  should  not 
be  larger  than  the  100-cc.  or  125-cc.  size,  put  about  5  grams 
caustic  potash,  dissolved  in  10-15  cc.  water,  and,  after  the  solu- 
tion has  become  quite  cold,  add  a  few  small  pieces  of  phosphorus 
the  size  of  a  pea,  and  push  the  stopper  in  tight.  Pass  hydrogen 


FIG.  54. 

free  from  air  for  some  time  through  the  apparatus  from  the  gen- 
erating-flask  A  until  all  the  air  is  displaced  ;  then  disconnect  at 
I),  leaving  the  rubber  tube,  closed  by  the  pinch-cock,  on  the  tube 
which  enters  the  flask.  Gently  heat  the  contents  of  the  retort, 
when  gradually  a  gas  will  bo  evolved  and  will  escape  through  the 
water  in  C.  As  each  bubble  comes  in  contact  with  the  air  it 
takes  fire,  and  the  products  of  combustion  arrange  themselves  in 
rings  which  become  larger  as  they  rise.  They  are  extremely 
beautiful,  particularly  if  the  air  of  the  room  is  quiet.  Both  the 
phosphorus  and  the  hydrogen  combine  with  oxygen  in  the  act  of.' 
burning.  See  Experiment  121. 


262  INTRODUCTION    TO   CHEMISTRY. 

Phosphine  itself  does  not  Take  Fire  Spontaneously.— 
The  spontaneous  inflammability  of  phosphine  has  been 
found  to  be  due  to  the  presence  of  a  small  quantity  of 
another  compound  of  phosphorus  and  hydrogen  which  is 
formed  by  the  action  of  phosphorus  on  caustic  potash. 
This  is  a  liquid  and  has  the  composition  P2H4.  It  is 
decomposed  by  exposure  to  light,  so  that  phosphine  which 
is  thus  exposed  loses  the  power  to  take  fire  by  contact  with 
the  air. 

EXPERIMENT  121.— Collect  a  good-sized  test-tube  full  of  the  gas 
by  displacement  of  water,  and  let  it  stand  over  water  for  a  few 
hours.  Now  remove  the  tube  from  the  water  and  let  the  gas 
escape  into  the  air.  Does  it  take  fire  ? 

Compounds  of  Phosphorus  with  Oxygen  and  with  Hy- 
drogen and  Oxygen. — The  product  formed  by  the  direct 
combination  of  phosphorus  and  oxygen  under  ordinary 
circumstances  has  the  composition  expressed  by  the 
formula  P205.  This  combines  with  water  in  different  pro 
portions,  forming  two  distinct  acids,  known  as  metaphos- 
phoric  and  orthopkosphoric  acids  : 

P,0,+  H,0    =         2HP03; 

Metaphosphoric  acid. 

P205  +  3H20  =         2H3P04. 

Orthophosphoric  acid. 

Orthophosphoric  or  Ordinary  Phosphoric  Acid,  H8P04, 

is  the  principal  compound  of  phosphorus.  It  is  the  final 
product  of  the  action  of  air  and  moisture  on  the  element. 
As  has  been  stated,  it  occurs  in  nature  as  the  calcium  salt; 
in  phosphorite  and  apatite.  This  salt  is  also  the  chief 
constituent  of  bone-ash. 

It  can  be  made  by  treating  bone-ash  with  sulphuric  acid, 
and  by  oxidizing  phosphorus. 

It  is  a  solid  crystallized  substance. 


METAPHOSPHORIC  AND  PYROPHOSPHORIC  ACIDS.   263 

Phosphoric  acid  has  the  power  of  forming  three  distinct 
salts  with  the  same  metal.  It  is  hence  called  tribasic. 
With  sodium,  for  example,  it  forms  the  three  salts  Na3P04 , 
Na2HP04,  and  NaH2P04.  Its  normal  calcium  salt — that 
i..<  to  say,  the  one  in  which  calcium  is  substituted  for  all  the 
three  hydrogen  atoms — has  the  formula  Cas(POJ2,  three 
bivalent  calcium  atoms  taking  the  place  of  six  atoms  of 
hydrogen. 

[Write  the  equation  expressing  the  action  that  takes 
place  when  sulphuric  acid  decomposes  normal  calcium 
phosphate,  forming  calcium  sulphate  and  phosphoric  acid.  ] 

Metaphosphorie  Acid,  HP03. — When  phosphoric  acid  is 
heated  to  a  sufficiently  high  temperature,  it  loses  hydrogen 
and  oxygen  in  the  form  of  water  and  yields  metaphosphoric 
acid  : 

H3P04  =  HP03  -f  H20. 

Metaphosphoric  acid  is  the  substance  that  is  sold  under 
the  name  of  glacial  phosphoric  acid.  It  is  made  by  evapo- 
rating solutions  of  phosphoric  acid  down  to  dryness  and 
heating  the  residue. 

Pyrophosphoric  Acid,  H4P807. — When  a  salt,  like  ordi- 
nary sodium  phosphate,  HNa2P04,  is  heated,  it  loses  water 
and  yields  a  salt  of  pyrophosphoric  acid : 

2HNa,P04  =  Na4Pa07  -f  H20. 

It  will  thus  be  seen  that  ordinary  phosphoric  acid  by 
losing  water  yields  pyrophosphoric  acid,  H4P207,  and 
metaphosphoric  acid,  HP03.  Both  of  these  acids  take  up 
water  and  are  reconverted  into  ordinary  phosphoric  acid : 

HP03  -f  H20  =  H3P04,     and 
H4P207  +  H,0  -  2H,P04. 


264  INTRODUCTION    TO   CHEMISTRY. 

Phosphorous  Acid,  H8P03. — This  acid  is  formed  by  allow- 
ing moist  air  to  act  on  phosphorus.  There  is  an  oxide, 
P203 ,  which  bears  to  the  acid  the  same  relation  that  phos- 
phorus pentoxide  bears  to  phosphoric  acid : 

P205+3H20  =2HJP04; 
P203  +  3H20  =  2H3P03. 

Arsenic,  As  (At.  Wt.  75). — Arsenic  occurs  in  nature  in 
combination  with  metals — as,  for  example,  iron,  copper, 
cobalt,  nickel,  etc. — and  in  combination  with  oxygen,  in 
the  form  of  the  trioxide  As203. 

It  is  generally  obtained  by  heating  arsenical  pyrites, 
FeAsS,  when  the  arsenic  separates  from  the  iron  and  sul- 
phur : 

FeAsS  =  FeS  +  As. 

It  is  also  made  by  reducing  arsenic  trioxide : 
As203  +  30  =  SCO  +  2As. 

It  has  a  metallic  lustre.  When  heated  to  a  high  tem- 
perature in  the  air  it  takes  fire,  and  burns  with  a  bluish 
flame,  giving  off  fumes  which  have  the  odor  of  garlic  and 
are  poisonous. 

It  combines  directly  with  most  elements.  In  the  ele- 
mentary form  it  is  not  poisonous,  but  when  oxidized  it 
becomes  so. 

Arsine,  Arseniuretted  Hydrogen,  AsH3.  —  This  com- 
pound is  analogous  to  ammonia  and  phosphine.  It  is 
made  by  the  action  of  nascent  hydrogen  [What  is  nascent 
hydrogen  ?]  on  the  compounds  of  arsenic  with  oxygen,  as 
when  these  compounds  are  brought  into  a  vessel  contain- 
ing zinc  and  sulphuric  acid. 

EXPERIMENT  122. — The  gas  formed  in  this  experiment  is  poi- 
sonous ! — Arrange  an  apparatus  as  shown  in  Fig.  55.  Put  some 


URSINE. 


265 


granulated  zinc  in  the  small  flask  and  pour  dilute  sulphuric  acid 
on  it.     When  the  air  is  all  out  of  the  vessel  and  the  hydrogen  is 


FIG.  55. 

lighted,  add  slowly  a  little  of  a  solution  of  arsenic  trioxide,  As2O3, 
in  dilute  hydrochloric  acid.  The  appearance  of  the  flame  will  soon 
change,  becoming  paler,  with  a  slightly  bluish  tint,  and  giving  off 
white  fumes.  (See  Experiment  123.) 

Properties  of  Arsine. — Arsine  is  a  colorless  gas  which  is 
poisonous  and  has  an  unpleasant  odor.  When  lighted  it 
burns  with  a  bluish-white  flame,  forming  arsenic  trioxide 
and  water.  It  is  very  unstable,  breaking  up  into  arsenic 
and  hydrogen  when  heated.  "When  a  cold  object,  as  a 
piece  of  porcelain,  is  brought  into  the  flame  of  burning 
arsine,  the  arsenic  is  deposited  in  the  form  of  a  dark  spot. 
This  fact  is  taken  advantage  of  for  the  purpose  of  testing 
for  arsenic  in  examining  the  stomach  and  other  viscera  in 
a  case  of  suspected  poisoning.  The  method  is  known  as 
Marsh's  test,  as  it  was  devised  by  a  chemist  by  the  name 
of  Marsh. 

EXPERIMENT  123. — Into  the  flame  of  the  burning  hydrogen  and 
arsine  produced  in  the  last  experiment  introduce  a  piece  of  por- 


266  INTRODUCTION    TO   CHEMISTRY. 

celain,  as  the  bottom  of  a  small  porcelain  dish  or  a  crucible,  and 
notice  the  appearance  of  the  spots.  Heat  by  means  of  a  Bunsen 
burner  the  tube  through  which  the  gas  is  passing,  which  should 
be  of  hard  glass.  Just  in  front  of  the  heated  place  a  thin  layer 
of  metallic  arsenic,  commonly  called  a  mirror  of  arsenic,  will 
be  deposited.  This  deposit  is  due  to  the  direct  decomposition 
of  the  arsine  into  arsenic  and  hydrogen  by  heat.  [Compare 
ammonia,  phosphine,  and  arsine  with  reference  to  their  stability.] 
Arsine  has  no  basic  properties,  differing  markedly  in 
this  respect  from  ammonia.  Phosphine,  as  has  been 
stated,  has  weak  basic  properties. 

Arsenic  Trioxide,  As203. — When  arsenic  is  bnrned  in 
the  air  or  in  oxygen  it  forms  the  trioxide.  [Compare  with 
phosphorus  in  this  respect.]  This  substance,  which  is 
generally  called  arsenic,  is  made  by  heating  compounds  of 
arsenic  and  metals  in  contact  with  the  air.  Under  these 
circumstances,  both  the  metal  and  the  arsenic  are  oxidized, 
and  the  oxide  of  arsenic,  being  volatile,  passes  off  and  is 
condensed  and  collected  in  large  brick  chambers. 

It  is  a  colorless,  amorphous,  glassy  mass.  It  is  difficultly 
soluble  in  water,  more  easily  in  hydrochloric  acid.  It  has 
a  weak,  disagreeably  aweet  taste,  and  is  very  poisonous. 
It  is  probably  more  frequently  used  as  a  poison  than  any 
other  substance.  Minute  quantities  can  be  detected  by 
the  chemist  with  absolute  certainty. 

The  oxide  is  easily  reduced  by  means  of  carbon. 

EXPERIMENT  124.— Mix  together  about  equal  small  quantities 
of  arsenic  trioxide  and  finely-powdered  charcoal.  Heat  the  mix- 
ture in  a  small  dry  tube  of  hard  glass,  closed  at  one  end.  The 
arsenic  which  is  set  free  will  be  deposited  on  the  walls  of  the  tube 
in  the  form  of  a  mirror,  like  that  obtained  in  Experiment  123. 

Acids  of  Arsenic. — Arsenic  forms  with  oxygen  and  hy- 
drogen an  acid  of  the  formula  H3As04 ,  known  as  arsenic 
acid,  which  is  analogous  to  orthophosphoric  acid.  When 
heated,  it  undergoes  changes  similar  to  those  referred  to 


ANTIMONY—STIBINE.  267 

in  connection   with  phosphoric  acid,  the  products  being 
metarsenic  acid,  HAs03 ,  and  pyroarsenic  acid,  H4As207. 

When  arsenic  trioxide  is  treated  with  bases  in  solution, 
salts  of  arsenious  acid,  or  the  arsenites,  are  formed.  The 
formula  of  the  potassium  salt  is  K3As03.  The  acid  HsAs03 
differs  from  arsenic  acid,  H3As04,  by  one  atom  of  oxygen 
in  the  molecule. 

Antimony,  Sb  (At.  Wt.  120). — This  element  occurs  most 
frequently  in  combination  with  sulphur  as  the  sulphide 
Sb2S3.  It  is  a  silver- white,  metallic-looking  substance. 
At  ordinary  temperature  it  is  riot  changed  by  contact  with 
the  air;  but  when  heated  to  a  sufficiently  high  temperature 
ki  the  air  it  takes  fire  and  burns,  forming  the  white  oxide. 

EXPERIMENT  125.— Heat  a  small  piece  of  antimony  on  charcoal 
by  means  of  the  blowpipe.  Notice  the  formation  of  the  white 
coating  on  the  charcoal  around  the  place  where  the  substance 
burns.  What  difference  is  there  between  the  conduct  of  anti- 
mony and  arsenic  before  the  blowpipe?  See  whether  you  can 
distinguish  between  antimony  and  arsenic  by  means  of  the  blow- 
pipe. 

Stibine,  Antimoniuretted  Hydrogen,  SbH3. — This  com- 
pound is  made  in  the  same  way  as  arsine. 

EXPERIMENT  126. — Make  some  stibine,  using  a  solution  of  tar- 
tar emetic. 

Its  properties  are  very  much  like  those  of  arsine.  It 
burns  with  a  similar  flame  and  is  decomposed  in  the  same 
way. 

EXPERIMENT  127. — Introduce  a  piece  of  porcelain  into  the  flame 
and  notice  the  deposit  or  antimony  spot.  It  is  darker  and  more 
smoky  than  the  arsenic  spot.  There  are  other  differences  in 
properties  by  which  they  can  be  distinguished  from  each  other 
with  absolute  certainty. 

Acids  of  Antimony. — Antimony  forms  acids  resembling 
phosphoric,  mctaphosphoric,  and  pyrophosphoric  acids. 


268  INTRODUCTION    TO   CHEMISTRY. 

Antimony  as  a  Base-forming  Element. — Antimony  not 
only  forms  acids  with  hydrogen  and  oxygen,  but  it  also 
forms  bases.  These  bases  neutralize  acids  and  form  salts 
in  which  antimony  takes  the  place  of  the  hydrogen  of  the 
acids.  Some  of  these  salts  are  rather  complicated  in 
composition,  and  it  would  lead  too  far  to  discuss  them 
here.  It  is  sufficient  for  the  present  to  recognize  the  im- 
portant fact  that  one  and  the  same  element  has  the  power 
to  form  acids  and  bases. 

Antimony,  however,  is  not  the  only  element  thus  far 
studied  which  has  this  double  power.  The  compounds  of 
nitrogen  with  hydrogen  and  oxygen  have,  in  general,  acid 
properties,  but  ammonia  has  strongly  basic  properties. 
We  see,  therefore,  that  when  nitrogen  is  combined  with 
hydrogen  the  product  has  basic  properties,  while  when 
combined  with  hydrogen  and  oxygen  in  forms  in  which 
the  oxygen  is  in  excess  the  products  are  acids.  The  same 
is  true  to  some  extent  of  phosphorus. 

At  the  same  time,  neither  the  element  nitrogen  nor  the 
element  phosphorus  itself  has  the  power  to  take  the  place 
of  the  hydrogen  of  acids,  and  this  power  antimony  has. 

Bismuth,  Bi  (At.  Wt.  208.5). — Bismuth  is  not  abundant 
nor  widely  distributed  in  nature.  It  occurs  for  the  most 
part  native,  or  uncombined,  in  veins  of  granite  or  clay 
slate.  It  occurs  also  as  the  oxide  Bi203,  and  as  the  sul- 
phide Bi2S3.  It  is  a  hard,  brittle,  reddish-white  substance 
with  a  metallic  lustre.  It  looks  very  much  like  antimony, 
but  is  distinguished  from  it  by  its  reddish  tint.  At  ordi- 
nary temperature  it  remains  unchanged  in  the  air,  but 
when  heated  to  redness  it  burns  with  a  bluish  flame,  form- 
ing the  yellow  oxide  Bi203. 

EXPERIMENT  128. — Heat  a  small  piece  of  bismuth  on  charcoal 
by  means  of  the  blowpipe.  Compare  the  result  with  the  results 
obtained  with  antimony  and  with  arsenic. 


GENERAL  REMARKS  ON   THE  NITROGEN  GROUP.    269 

Salts  of  Bismuth.—  Bismuth  forms  two  classes  of  salts, 
known  as  bismuth  and  bismuthyl  salts.  In  the  former  the 
bismuth  acts  as  a  trivalent  metal,  taking  the  place  of  three 
atoms  of  hydrogen  as  in  the  nitrate  Bi(N03)3.  In  the 
bismuthyl  salts  the  group  bismuthyl,  BiO,  takes  the  place 
of  one  atom  of  hydrogen,  as  in  bismuthyl  nitrate  BiO(N03). 
Antimony  forms  salts  similar  to  both  these  classes. 

Bismuth  Nitrates. — When  bismuth  is  dissolved  in  nitric 
acid  and  the  solution  evaporated  to  dryness  the  salt 
Bi(N03)3  +  10H20  is  obtained.  This  salt  is  decomposed 
when  heated,  and  by  water,  forming  basic  nitrates  of 
bismuth.  These  differ  in  composition  according  to  the 
method  of  preparation,  but  all  are  formed  by  incomplete 
neutralization  of  the  base  Bi(OH)3.  The  basic  nitrate  of 
oismuth,  or  the  subnitrate,  as  it  is  called  in  pharmacy,  is 
much  used  in  medicine  as  a  remedy  in  dysentery  and 
cholera.  It  is  also  used  as  a  cosmetic. 

There  are  three  rare  elements  which  in  their  chemical 
conduct  resemble  the  members  of  the  nitrogen  group. 
These  are  vanadium,  colunibium,  and  tantalum.  It  would 
be  unprofitable  to  undertake  their  study  at  this  stage. 

General  Remarks  on  the  Characteristics  of  the  Nitrogen 
Group. — The  resemblance  between  nitrogen  and  phos- 
phorus is  seen  especially  in  the  compounds  ammonia  and 
phosphine.  Between  the  oxides  of  nitrogen  and  of  phos- 
phorus the  resemblance  is  not  striking.  There  are  two 
oxides  of  nitrogen, — the  trioxide,  N203,  and  the  pent- 
oxide,  N205, — which  in  composition  correspond  to  the 
two  oxides  of  phosphorus,  P203  and  P205.  But  while  the 
pentoxide  of  phosphorus  is  the  most  common  oxide  of  this 
element,  the  pentoxide  of  nitrogen  is  obtained  with  greater 
difficulty  than  any  of  the  other  oxides  of  nitrogen.  There 
are  no  compounds  of  phosphorus  analogous  to  the  three 
principal  oxides  of  nitrogen, — nitrous  oxide,  N20;  nitric 


270  INTRODUCTION    TO   CHEMISTRY. 

oxide,  NO;  and  nitrogen  peroxide,  N02.  There  is  no 
acid  of  phosphorus  corresponding  to  nitrous  acid,  HNO, . 
and  there  are  no  compounds  of  nitrogen  analogous  to 
phosphoric  acid,  H3P04 ,  and  pyrophosphoric  acid, 
H4P207.  Nitric  acid,  HN03,  and  metaphosphoric  acid, 
HP03 ,  have  analogous  compositions. 

The  resemblance  between  phosphorus,  arsenic,  and  anti- 
mony is  much  more  striking  than  that  between  nitrogen 
and  phosphorus.  This  resemblance  has  already  been 
noted  in  the  acids  formed  by  the  three  elements,  and  in 
their  hydrogen  compounds,  PII3 ,  AsH3 ,  and  SbII3 ,  all  of 
which  are  analogous  to  ammonia.  The  same  resemblance 
is  seen  in  their  oxides,  P203,  P205,  As203,  As.,03,  and 
Sb203,  Sb205.  Their  compounds  with  chlorine  and  the 
other  members  of  the  chlorine  group  are  also  strikingly 
similar.  Antimony  and  bismuth  closely  resemble  each 
other  in  some  respects.  The  latter  forms  two  oxides, 
Bi20s,  and  Bi205,  and  forms  salts  in  the  same  way  that 
antimony  does,  but  the  element  has  very  weak  acid 
properties.  The  elements  of  the  nitrogen  group  are 
trivalent  in  some  compounds,  as  in  NH3,  PIT3,  AsII3, 
PC13,  AsClg,  etc.;  and  quinquivalent  in  others,  as  ir 
NH4C1,  in  which  the  nitrogen  is  believed  to  hold  in  com 
bination  four  atoms  of  hydrogen  and  one  atom  of  chlorine, 
in  PC15,  etc.,  etc. 

The  atomic  weights  are  N  =  14.04;  P  =  31;  As  =  75; 
Sb  -  120;  Bi  =  208.5.  These  figures  do  not  all  bear 
simple  relations  to  one  another,  but  between  the  .atomic 
weights  of  phosphorus,  arsenic,  and  antimony  there  exists 
a  relation  similar  to  that  already  noticed  between  the 
atomic  weights  of  chlorine,  bromine,  and  iodine,  and  sul- 
phur, selenium,  and  tellurium.  Thus,  P  =  31,  Sb  =  120, 
and  As  =  75 : 

31  +  120  _755 
— g—       -  75.5. 


BORON.  2  7 1 

Again,  between  the  atomic  weights  of  phosphorus,  anti- 
mony, and  bismuth  the  same  relation  exists.  Thus, 
P  =  31,  Sb  =  120,  Bi  =  208.5: 

31  +f 8-5  =  119.75. 

z 

Boron,  B  (At.  Wt.  11). — Boron  may  conveniently  be 
studied  in  connection  with  the  nitrogen  group,  as  some  of 
its  properties  suggest  those  of  the  members  of  the  group. 
At  the  same  time,  it  presents  peculiarities  which  distin- 
guish it  from  these  elements.  Boron  occurs  in  nature  in 
the  form  of  boric  acid,  or  as  salts  of  this  acid,  particularly 
the  sodium  salt,  or  borax.  It  is  prepared  by  treating  the 
oxide,  B203 ,  at  a  very  high  temperature  with  sodium  or 
aluminium.  Under  proper  conditions  it  is  obtained  in 
the  form  of  crystals  which  are  almost  as  hard  as  diamonds. 

At  a  red  heat  uncrystallized  boron  combines  with  nitro- 
gen very  readily.  The  crystallized  variety  can  be  heated 
to  a  high  temperature  in  the  air  without  changing.  These 
properties  distinguish  boron  from  the  members  of  the 
nitrogen  family,  all  of  which,  with  the  exception  of 
nitrogen,  combine  with  oxygen.  Boron  combines  with 
chlorine,  forming  the  chloride  BC13,  analogous  to  the 
chlorides  of  phosphorus  and  arsenic,  PC13  and  AsCl3. 

Boric  Acid,  H3B03. — The  chief  compound  of  boron  is 
boric  acid.  It  occurs  in  nature  in  large  quantities, 
issuing  from  the  earth  with  water-vapor  in  some  localities, 
particularly  in  Tuscany.  The  jets  of  steam  charged  with 
boric  acid,  which  are  called  suffioni,  are  conducted  into 
tanks  of  water,  in  which  the  acid  condenses.  The  solution 
is  evaporated  by  means  of  the  heat  of  the  natural  steam- 
jets,  and  finally  the  acid  crystallizes  out.  The  acid  is  also 
obtained  from  a  natural  magnesium  salt  called  boracite, 
and  from  borax,  which  is  a  sodium  salt. 


2 72  INTRODUCTION   TO  CHEMISTRY. 

When  heated  to  100°,  boric  acid  loses  water  and  is  con- 
verted into  metdboric  acid,  HB02: 

H3B03  =  HB02  +  H20. 

[What  is  the  analogous  change  of  phosphoric  acid  ?] 
The  acid  thus  obtained  is  analogous  to  nitrous  acid  in 
composition. 

When  heated  higher,  a  larger  proportion  of  water  is 
given  off,  and  an  acid  of  the  formula  H2B407,.or  tetraboric 
acid,  is  left  behind.  This  is  the  form  of  boric  acid  from 
which  borax  is  derived.  The  formula  of  borax  is  Na2B407 
-J-  10H20.  The  relation  between  tetraboric  acid  and 
normal  boric  acid  is  shown  by  the  equation 

4H3B03  =  H2B407  +  5H20. 

Heated  to  a  still  higher  temperature,  boric  acid  loses  all 
of  its  hydrogen  in  the  form  of  water,  and  boron  trioxide, 
or  boric  anhydride,  B203,  is  left  behind.  [What  is  the 
significance  of  the  name  boric  anhydride  ?] 

When  a  solution  of  borax  is  treated  with  sulphuric  acid, 
boric  acid  is  set  free,  and  crystallizes  out  if  the  solution  is 
concentrated  enough. 

EXPERIMENT  129.— Make  a  hot  solution  of  30  grams  crystal- 
lized borax  in  120  cc.  water.  Add  slowly  10  grams  concentrated 
sulphuric  acid.  On  cooling,  the  boric  acid  will  crystallize  out. 
[What  evidence  have  you  that  the  substance  which  crystallizes 
out  of  the  solution  is  not  borax  ?]  Try  the  solubility  in  alcohol 
of  specimens  of  each.  [Is  there  any  difference?]  Treat  a  few 
crystals  of  borax  with  about  10  cc.  alcohol ;  pour  off  the  alcohol 
and  set  fire  to  it.  Treat  a  few  crystals  of  boric  acid  in  the  same 
way.  [What  difference  do  you  observe  ?] 

Boric  Anhydride,  B203,  when  heated,  melts  and  forms 
a  clear  glass.  This  has  the  power  to  dissolve  many  sub- 
stances which  ordinary  solvents  will  not  dissolve,  and  some 
of  the  solutions  thus  formed  are  colored.  This  fact  is 


BORIC  ANHYDRIDE.  273 

taken  advantage  of  in  the  laboratory  for  the  purpose  of 
detecting  the  presence  of  those  substances  which  form 
colored  solutions.  The  method  of  work  consists  in 
melting  a  little  boric  acid  or  borax  in  a  loop  of  platinum 
wire,  and  then  bringing  a  minute  particle  of  the  substance 
to  be  examined  in  coittact  with  the  glass  bead  thus  formed. 
When  heated  before  the  blowpipe  it  will  generally  dissolve. 
By  holding  the  bead  in  the  oxidizing  flame  of  the  blowpipe 
the  substance  in  solution  may  be  oxidized,  and  by  holding 
it  in  the  reducing  name  it  may  be  reduced.  Changes  of 
color  may  thus  be  produced  which  will  aid  us  in  determin- 
ing what  substance  we  have  to  deal  with.  This  method 
is  valuable  for  the  purposes  of  analysis. 

When  an  alcoholic  solution  of  boric  acid  is  lighted,  it 
burns  with  a  green  flame.  The  salts  of  boric  acid  do  not 
color  the  alcohol  flame.  [What  evidence  have  you  had  of 
the  truth  of  this  statement  ?] 

Boron  is  trivalent  in  most  of  its  compounds,  as  in  the 
chloride,  BC18. 


CHAPTER   XVIII. 
THE   CARBON    GROUP:    CARBON   AND   SILICON. 

TITANIUM ZIRCONIUM CERIUM THORIUM. 

Silicon,  Si  (At.  Wt.  28.4).— We  have  already  learned 
how  important  a  part  carbon  plays  in  animate  nature.  It 
is  interesting  to  note  that  silicon,  which  in  some  respects 
resembles  carbon  from  a  chemical  point  of  view,  is  one  of 
the  most  important  constituents  of  the  mineral  or  in- 
organic parts  of  the  earth.  It  occurs  chiefly  in  the  form 
of  the  oxide,  Si02,  commonly  called  silica,  or  silicon 
dioxide;  and  in  combination  with  oxygen  and  several  of 
the  common  metals,  particularly  sodium,  potassium,  alu- 
minium, and  calcium,  in  the  form  of  silicates.  Next  to 
oxygen,  silicon  is  the  most  abundant  element  in  nature. 
There  are  extensive  mountain-ranges  consisting  almost 
entirely  of  silicon  dioxide,  Si02,  in  the  form  known  as 
quartz  or  quart zite.  Other  ranges  are  made  up  of  silicates, 
which  are  compounds  formed  by  a  combination  of  silicon 
dioxide  and  bases.  The  clay  of  valleys,  river-beds,  etc., 
also  contains  silicon  in  large  quantity,  while  the  sand 
found  so  abundantly  at  the  sea-shore  is  mostly  silicon 
dioxide,  Si02. 

Silicon  is  never  found  in  the  free  state,  and  it  is  difficult 
to  decompose  the  oxide,  Si02 ,  in  such  a  way  as  to  get  the 
element,  though  it  can  be  accomplished  by  heating  the 
oxide  with  potassium  or  magnesium.  Under  proper  con- 
ditions silicon  can  be  obtained  in  the  form  of  crystals 

274 


SILICIC  ACID  275 

that  have  a  gray  color  and  are  harder  than  glass.  It  is 
not  acted  upon  by  the  strongest  acids,  nor  when  heated  in 
a  current  of  oxygen. 

With  hydrogen,  silicon  forms  a  gaseous  compound  of 
the  formula  SiH4;  it  combines  with  chlorine,  forming 
SiCl4,  and  with  fluorine,  forming  SiF4.  The  fluoride  has 
already  been  referred  to  in  connection  with  the  action  of 
hydrofluoric  acid  on  silicates.  We  have  seen  that  hydro- 
fluoric acid  dissolves  silicates — as,  for  example,  glass — in 
consequence  of  the  action  of  the  acid  on  silicon  dioxide, 
which  is  represented  thus : 

Si02  +  4HF  =  SiF4  -f  2H20. 
The  silicon  fluoride  passes  off  in  the  form  of  gas. 

Silicides  are  compounds  of  silicon  with  other  elements, 
as,  for  example,  with  carbon.  These  two  elements  com- 
bine forming  an  interesting  compound,  carbon  silicide, 
CSi,  which  is  manufactured  on  the  large  scale  under  the 
name  of  carborundum.  It  is  made  by  heating  a  mixture 
of  quartz  sand,  coke,  and  common  salt  in  the  electric 
furnace.  It  is  a  very  stable  substance,  and  is  extremely 
hard,  so  that  it  is  used  as  a  substitute  for  emery. 

Silicic  Acid. — There  are  several  varieties  of  silicic  acid, 
all  of  which  are,  however,  derived  from  an  acid  of  the 
formula  H4Si04,  or  normal  silicic  acid.  When  this  is  set 
free  from  its  salts,  it  loses  water,  and  is  changed  to  ordi- 
nary silicic  acid,  H2Si03 : 

H4Si04  =  H2SiOs  +  H20. 

When  heated,  this  second  form  of  silicic  acid  is  converted 
into  the  dioxide  Si02: 

HaSi08  =  SiO,  +  H30. 


2  76  INTRODUCTION   TO   CHEMISTRY. 

Most  of  the  ordinary  silicates  are  derived  from  the  acid 
of  the  formula  H2Si03.  [What  is  the  formula  of  carbonic 
acid  ?  Under  what  circumstances  does  carbonic  acid  break 
down  into  carbon  dioxide  and  water  ?]  Other  silicic  acids 
are  obtained  by  heating  ordinary  silicic  acid.  Thus, 
under  the  proper  conditions  an  acid  of  the  formula 
H2Si205  ,  and  one  of  the  formula  H4Si308  ,  are  obtained  : 


3H,SiOs  •=  H4Si308  4-  H20. 

These   are   called   poly  silicic   acids.     Some   of   these   are 
found  in  nature.      Opal  is  the  best-known  example. 

Silicon  Dioxide,  Silicic  Anhydride,  Si02.  —  As  already 
stated,  this  substance  occurs  very  abundantly  in  nature 
and  in  many  different  forms.  Quartz,  or  rock  crystal,  is 
pure  crystallized  silicon  dioxide;  quartzite  is  a  coarser- 
grained  substance  made  up  of  small  crystals  of  quartz, 
usually  colored.  Agate,  amethyst,  and  carnelian  are 
varieties  of  quartz  colored  by  foreign  substances. 

Silicon  dioxide  is  insoluble  in  water  and  acids.  It  is 
soluble  in  hydrofluoric  acid,  as  has  been  stated.  Glass 
consists  of  salts  of  silicic  acid,  usually  of  the  sodium  or 
potassium  salts  and  calcium  salts. 

Comparison  of  Carbon  and  Silicon.  —  The  two  principal 
elements  of  this  family  resemble  each  other  in  the  com- 
position of  some  of  their  simplest  compounds,  as  carbon 
dioxide,  C02  ,  and  silicon  dioxide,  Si02;  carbonic  acid, 
H2C03,  and  silicic  acid,  H2Si03;  marsh-gas,  CH4,  and 
silicon  hydride,  SiH4;  carbon  tetrachloride,  CC14,  and 
silicon  tetrachloride,  SiCl4.  On  the  other  hand,  they 
present  marked  points  of  difference.  "Each  yields  a  large 
number  of  derivatives,  but  the  derivatives  of  carbon  bear 
to  the  element  relations  entirely  different  from  those 


RARE  ELEMENTS   OF   THE   CARBON  GROUP.         277 

which  the  derivatives  of  silicon  bear  to  this  element.  Thb 
compounds  of  carbon  can  all  be  shown  to  be  derived  from 
the  hydrocarbons;  that  is  to  say,  they  may  be  regarded  as 
formed  from  the  hydrocarbons  by  a  comparatively  simple 
set  of  changes,  while  most  of  the  compounds  containing 
silicon  are  derivatives  of  silicic  acid. 

Rare  Elements  of  this  Group. — The  rare  elements  tita- 
nium, zirconium,  cerium,  and  thorium  resemble  silicon  in 
their  chemical  conduct.  They  form  oxides  of  the  formulas 
Ti02,  Zr02,  Oe02,  and  Th02  which  are  analogous  to  sili- 
con dioxide.  Titanium  occurs  in  nature  principally  as 
the  dioxide,  and  forms  the  three  minerals  rutile,  brookite, 
and  anatase.  Zirconium  occurs  in  nature  as  zircon,  which 
is  a  silicate  of  the  formula  ZrSi04. 


CHAPTER   XIX. 

BASE-FORMING     ELEMENTS.— GENERAL    CONSIDERA- 
TIONS. 

Introductory. — At  the  end  of  Chapter  XIV  is  this  sen- 
tence: "  After  the  acid-forming  elements  have  been 
studied,  the  base-forming  elements  will  be  taken  up  in  a 
similar  way;  but,  as  will  be  seen,  the  chemistry  of  the 
acid-forming  elements  exhibits  more  variety,  and  is  hence 
better  adapted  to  the  illustration  of  the  general  principles 
of  the  science  than  that  of  the  base-forming  elements,  so 
that  the  latter  need  not  be  treated  as  fully." 

The  significance  of  the  name  base-forming  elements  has 
been  explained.  It  is  simply  this:  The  compounds  of 
these  elements  with  hydrogen  and  oxygen  are  bases,  or, 
in  other  words,  have  the  power  to  neutralize  acids  and 
form  salts.  But  the  distinction  between  acid-forming  and 
base-forming  elements  is  not  a  sharp  one,  for  the  reason 
that  there  are  some  elements  that  occupy  an  intermediate 
position,  forming  both  acids  and  bases.  One  example  of 
this  kind  already  studied  is  antimony,  and  the  reason  why 
it  is  regarded  as  a  member  of  the  nitrogen  group  is  that 
it  is  unquestionably  closely  related  to  arsenic,  which  is  an 
acid-forming  element.  A  close  study  will  show  that  those 
elements  which  have  the  power  to  form  both  acids  and 
bases  are  related  to  one  of  the  four  groups  already  studied. 
There  are,  thus,  certain  elements  which  show  some 
resemblance  to  the  members  of  the  chlorine  group,  but 

278 


ORDER  OF  BASE-FORMING  ELEMENTS.  279 

nevertheless  act  principally  as  base-formers;  so,  too,  there 
are  certain  elements  which  resemble  the  members  of  the 
sulphur  group,  but  which  generally  form  bases.  In  a 
similar  way,  there  are  base-forming  analogues  of  the 
nitrogen  and  carbon  groups.  Those  elements  which  always 
act  as  base-formers  have  no  analogues  among  the  acid- 
forming  elements. 

Order  in  which  the  Base -forming  Elements  will  be 
Taken  up. — In  studying  the  base-forming  elements,  it 
appears  best  to  begin  with  those  which  have  the  most 
strongly  marked  character.  These  are  members  of 
Group  I,  as  shown  in  the  table  page  224.  It  further 
appears  best  to  adhere  as  closely  as  possible  to  the  arrange- 
ment in  the  periodic  system.  Accordingly  the  following 
order  will  be  observed  in  the  presentation  of  the  elements 
yet  to  be  studied : 

1.  The  Potassium  Group,  consisting  of  lithium,  sodium, 
potassium,  rubidium,  and  caesium. 

2.  The  Calcium  Group,  consisting  of  glucinum,  calcium, 
barium,  and  strontium. 

3.  The   Magnesium   Group,   consisting  of  magnesium, 
zinc,  and  cadmium. 

4.  The  Silver  Group,  consisting  of  silver,  copper,  and 
mercury. 

5.  The  Aluminium  Group,  of  which  aluminium  is  the 
only  well-known  member.     Allied  to  it  are  the  rare  ele- 
ments  gallium,    indium,    thallium,    scandium,    yttrium, 
lanthanum,  and  ytterbium. 

6.  The  Lead  Group,  consisting  of  germanium,  tin,  and 
lead. 

7.  The    Chromium    Group,    consisting    of    chromium, 
molybdenum,  and  tungsten.     The  members  of  this  group 
show  some  analogy  to  the  members  of  the  sulphur  group, 
as  will  be  pointed  out  under  chromium, 


280  INTRODUCTION   TO  CHEMISTRY. 

8.  The  Manganese  Group,  of  which  manganese  is  the 
only  representative.    There  are  some  points  of  resemblance 
between   manganese  and   the   members   of   the   chlorine 
group. 

9.  The   Iron    Group,   consisting   of  iron,    cobalt,  and 
nickel. 

10.  The   Palladium    Group,    consisting   of   palladium, 
ruthenium,  and  rhodium. 

11.  The  Platinum  Group,  consisting  of  osmium,  iridium, 
platinum,  and  gold. 

It  will  be  seen  at  once  that  there  are  many  more  base- 
forming  than  acid-forming  elements,  and  it  is  a  serious 
undertaking  to  become  thoroughly  acquainted  with  all  the 
elements  included  under  this  head.  In  order  to  get  a 
general  knowledge  of  the  principles  of  chemistry,  however, 
it  is  not  necessary  to  study  all  these  elements.  The 
chemist  must,  of  course,  familiarize  himself  to  some  extent 
with  all  of  them,  and  those  who  continue  the  study  of 
chemistry  hereafter  will  have  abundant  opportunity  to 
study  them  in  detail.  For  the  present  it  will  be  best  to 
confine  attention  to  a  few  of  the  representative  elements 
included  in  the  above  list.  A  knowledge  of  these  will 
make  it  possible  to  study  the  others  without  serious  diffi- 
culty, should  occasion  demand. 

Metallic  Properties. — It  has  long  been  customary  to 
divide  the  chemical  elements  into  two  classes, — the  metals 
and  the  non-metals.  This  classification  was  originally 
based  upon  differences  in  the  physical  properties  of  the 
elements,  the  name  metal  being  applied  to  those  elements 
which  have  what  is  known  as  a  metallic  lustre,  are  opaque, 
and  are  good  conductors  of  heat  and  electricity.  All  those 
elements  which  do  not  have  these  properties  were  called 
non-metals.  Gradually  the  name  metal  came  to  signify 
an  element  which  has  the  power  to  take  the  place  of  the 


OCCURRENCE  AND  EXTRACTION  OF  METALS.     281 

hydrogen  of  acids  and  form  salts,  and  the  name  non-metal 
to  signify  an  element  which  has  not  this  power.  This 
classification,  as  will  be  seen,  is  about  the  same  as  that 
made  use  of  in  this  book.  It  thus  appears  that,  in  general, 
elements  that  have  similar  physical  properties  have  also 
similar  chemical  properties. 

Occurrence  of  the  Metals. — One  of  the  first  questions 
that  suggests  itself  in  connection  with  each  element  is,  In 
what  forms  of  combination  does  it  occur  in  nature  ?  The 
chemical  elements  and  compounds  that  occur  ready-formed 
in  nature  are  called  minerals;  and  the  minerals  and  mix- 
tures of  minerals  from  which  the  metals  are  extracted  for 
practical  purposes  are  called  ores.  The  most  common  ores 
are  oxides  and  sulphides.  Examples  of  these  are  the  ores 
of  iron,  tin,  copper,  lead,  and  zinc.  The  carbonates  also 
occur  in  large  quantity  in  nature,  and  are  used  for  the 
purpose  of  preparing  some  of  the  metals.  The  carbonate 
of  zinc,  for  example,  is  a  valuable  ore  of  zinc. 

Extraction  of  Metals  from  their  Ores. — The  detailed 
study  of  the  methods  used  in  the  extraction  of  the  metals 
from  their  ores  is  the  object  of  metallurgy.  Besides  the 
methods  used  on  the  large  scale,  there  are  others  which  are 
only  used  in  the  laboratory.  The  most  common  method 
of  extracting  metals  from  their  ores  is  that  used  in  the  case 
of  iron,  which  consists  in  heating  the  oxides  with  charcoal 
or  coke.  If  the  ores  used  are  not  oxides  they  must  first 
be  converted  into  oxides  before  this  method  is  applicable. 
This  can  generally  be  accomplished  by  heating  the  ores  in 
contact  with  the  air.  Under  these  circumstances  the 
natural  carbonates,  sulphides,  and  hydroxides  are  con- 
verted into  oxides.  These  changes  are  illustrated  by  the 
following  equations: 


282  INTRODUCTION   TO  CHEMISTRY, 

FeC03  =  FeO  +  00,: 
2FeO  +  0  =  Fe30s; 
2FeS2  -f  110  =  Fe.,03  +  4S02; 
2Fe(OH)3  =  Fe203  -f  3H20. 

A  second  method  consists  in  reducing  the  oxide  by 
heating  it  in  a  current  of  hydrogen.  This  has  been  illus- 
trated in  the  action  of  hydrogen  upon  copper  oxide,  when 
the  following  reaction  takes  place : 

CnO  +  H2  =  H20  -f  Cu. 

The  method  is  efficient  for  many  oxides,  but  is  expensive 
and  is  not  used  on  the  large  scale. 

Another  method  of  extraction  consists  in  treating  the 
chloride  of  a  metal  with  sodium.  This  is  illustrated  in  the 
preparation  of  magnesium: 

MgCl,  +  2Na  =  Mg  +  SNaCl. 

Such  a  method  is  employed  only  in  case  it  is  impossible  or 
extremely  difficult  to  reduce  the  oxide. 

A  number  of  the  metals  are  obtained  by  the  action  of 
an  electric  current  upon  some  one  of  their  compounds  in 
molten  condition.  The  preparation  of  aluminium  is  a 
good  example  of  this. 

Besides  the  above  methods,  there  are  others  which  will 
be  described  under  the  individual  metals. 

The  Properties  of  the  Metals, — As  we  shall  find,  the 
metals  differ  very  markedly  from  one  another.  Some  are 
light,  floating  on  water,  as  lithium,  sodium,  etc.;  some 
are  extremely  heavy,  a«  lead,  platinum,  etc.  Some  com- 
bine with  oxygen  with  great  energy;  others  form  very 
unstable  compounds  with  oxygen.  Some  form  strong 
bases;  others  form  weak  bases.  In  general,  those  elements 
which  are  lightest,  or  which  have  the  lowest  specific 
gravity,  are  the  most  active  chemically,  while  those  which 


COMPOUNDS   OF   THE  MET4LS.  283 

have  the  highest  specific  gravity  are  the  least  active. 
Among  the  former  are  lithium,  sodium,  and  potassium; 
among  the  latter  are  lead,  gold,  and  platinum. 

Compounds  of  the  Metals.  —  The  compounds  of  the 
metals  may  be  conveniently  classified  as: 

a.  Compounds   with   fluorine,  chlorine,    bromine,  and 
iodine;  or  the  fluorides,  chlorides,  bromides,  and  iodides. 

b.  Compounds  with  oxygen,  and  with  oxygen  and  hy- 
drogen: or  the  oxides  and  hydroxides. 

c.  Compounds   with    sulphur,    and   with    suphur    and 
hydrogen;  or  the  sulphides  and  hydro  sulphides. 

d.  Compounds   with   nitrogen   and  with   the  acids   of 
nitrogen;  or  the  nitrides,  nitrates,  and  nitrites. 

e.  Compounds  with  the  acids  of  chlorine,  bromine,  and 
iodine;  or  the  chlorates,  bromates,  iodates,  hypochlorites, 
etc. 

/.  Compounds  with  the  acids  of  sulphur;  or  the  sul- 
phates, sulphites,  etc. 

g.  Compounds  with  carbon  and  with  carbonic  acid;  or 
the  carbides  and  the  carbonates. 

h.  Compounds  with  the  acids  of  phosphorus,  arsenic, 
and  antimony;  or  the  phosphates,  ar senates,  etc. 

i.   Compounds  with  silicic  acid;  or  the  silicates. 

j.   Compounds  with  boric  acid;  or  the  borates. 

Of  the  almost  infinite  number  of  compounds  belonging 
to  the  classes  above  referred  to,  only  a  comparatively  small 
number  will  be  treated  of  in  this  book.  It  is  more  im- 
portant to  become  acquainted  with  the  general  methods  of 
preparation  and  the  general  properties  of  these  compounds 
than  to  learn  details  concerning  many  individual  members 
of  each  class.  Only  those  compounds  will  be  treated  which 
illustrate  general  principles,  or  which,  owing  to  some 
application,  happen  to  be  of  special  interest. 

The  acids  of  which  the  salts  are  derivatives  are  already 


284  INTRODUCTION   TO   CHEMISTRY. 

known  to  us,  and  in  dealing  with  acids  frequent  reference 
has  been  made  to  the  methods  of  making  the  salts,  and  to 
some  of  their  most  important  properties.  It  will  be  well, 
before  taking  up  the  metals  systematically,  to  discuss  briefly 
the  general  methods  of  preparation,  and  the  general 
properties  of  the  different  classes  of  metallic  compounds. 
It  must  be  borne  in  mind,  however,  that  the  only  way  to 
become  familiar  with  these  substances  and  their  relations 
is  by  working  with  them  in  the  laboratory. 

Chlorides. — The  chlorides,  as  well  as  the  fluorides, 
bromides,  and  iodides,  may  be  regarded  as  the  salts  of 
hydrochloric,  hydrofluoric,  hydrobromic,  and  hydriodic 
acids,  or  simply  as  compounds  of  the  metals  with  the 
members  of  the  chlorine  group.  The  most  important  of 
these  compounds  are  the  chlorides,  and  these  well  illus- 
trate the  conduct  of  the  others. 

The  chlorides  are  made  by  treating  the  metals  with 
hydrochloric  acid  or  chlorine;  by  treating  an  oxide  or  a 
hydroxide  with  hydrochloric  acid;  by  treating  an  oxide 
with  chlorine  and  a  reducing  agent,  like  carbon ;  by  treat- 
ing a  salt  of  a  volatile  acid,  a  carbonate  for  example,  with 
hydrochloric  acid;  by  treating  a  salt  of  an  insoluble  acid 
with  hydrochloric  acid ;  by  adding  hydrochloric  acid  or  a 
soluble  chloride  to  a  solution  containing  a  metal  with 
which  chlorine  forms  an  insoluble  compound  ;  and  by 
adding  to  a  solution  of  a  chloride  a  salt  the  acid  of  which 
forms  with  the  metal  of  the  chloride  an  insoluble  salt, 
while  the  metal  contained  in  it  forms  with  chlorine  a 
soluble  chloride. 

Only  two  of  the  above  methods  are  peculiar  to  chlorides. 
These  are  the  treatment  of  the  metals  with  chlorine,  and 
the  treatment  of  oxides  with  chlorine  and  a  reducing 
agent.  The  others  involve  principles  which  are  also  in- 
volved in  the  preparation  of  all  salts,  and  they  may  there- 
fore be  treated  in  a  general  way. 


CHLORIDES.  285 

EXAMPLES.— Zinc  chloride  is  formed   by  treating  zinc 
with  hydrochloric  acid. 
[Write  the  equation.] 
Ferric  chloride  is  formed  by  treating  iron  with  chlorine : 

Fe  +  3C1  =  FeCl3. 

Calcium  chloride  is  formed  by  treating  lime  or  calcium 
cxide,  CaO,  with  hydrochloric  acid: 

CaO  +  2HC1  =  CaCl2  4-  H20. 

Sodium  chloride  is  formed  by  treating  sodium  hy- 
droxide, or  caustic  soda,  NaOH,  with  hydrochloric  acid: 

NaOH  +  HC1  =  NaCl  +  II20. 

[What  takes  place  when  caustic  soda  or  caustic  potash 
is  treated  with  chlorine  ?] 

Calcium  chloride  is  formed  when  calcium  carbonate, 
CaC03,  is  treated  with  hydrochloric  acid: 

CaC03  +  2HC1  =  CaCl2  +  C02  -f  H20. 

Silver  chloride  is  precipitated  when  hydrochloric  acid 
or  a  soluble  chloride  is  added  to  a  solution  containing  a 
silver  salt. 

EXPERIMENT  130. — Dissolve  a  small  crystal  of  silver  nitrate  in 
pure  water.  Add  to  a  small  quantity  of  this  solution  in  a  test- 
tube  a  few  drops  of  dilute  hydrochloric  acid.  The  white  substance 
thus  precipitated  is  silver  chloride,  AgCl.  To  another  small  por- 
tion of  the  solution  add  a  few  drops  of  a  dilute  solution  of  com- 
mon salt,  or  sodium  chloride,  NaCl.  The  white  substance  pro- 
duced in  this  case  is  also  silver  chloride.  Add  ammonia  to  each 
tube.  If  sufficient  is  added  the  precipitates  will  dissolve.  On 
adding  enough  hydrochloric  acid  to  these  solutions  to  combine 
with  all  the  ammonia,  the  silver  chloride  is  again  thrown  down. 
On  standing  exposed  to  the  light  both  precipitates  change  color, 
becoming  finally  dark  violet.  The  reactions  involved  in  the  above 


286  INTRODUCTION   TO   CHEMISTRY. 

experiments  are  these  :  In  the  first  place,  when  hydrochloric  acid 
is  added  to  silver  nitrate  this  reaction  takes  place  : 

AgNO3  +  HOI  =  AgCl  +  HNO3. 
When  sodium  chloride  is  added  this  reaction  takes  place : 

AgNO,  4-  NaCl  =  AgCl  +  NaNO,. 

In  the  first  reaction  nitric  acid  is  set  free  ;  in  the  second,  the 
sodium  and  silver  exchange  places.  In  addition  to  the  insoluble 
silver  chloride,  there  is  formed  at  the  same  time  the  soluble  salt, 
sodium,  nitrate.  On  adding  ammonia  the  silver  chloride  forms 
with  it  a  compound  which  is  soluble  in  water  ;  and,  on  adding  an 
acid,  the  ammonia  combines  with  this,  leaving  the  silver  chloride 
uncombined  and  therefore  insoluble. 

General  Properties  of  the  Chlorides, — Most  of  the  chlo- 
rides of  the  metals  are  soluble  iii  water  without  decom- 
position, though  many  of  them  are  decomposed  when 
heated  to  a  sufficiently  high  temperature  with  water. 
Silver  chloride,  AgOl,  and  mercurous  chloride,  HgCl,  are 
insoluble  in  water.  Lead  chloride,  PbCl2,  is  difficultly 
soluble  in  water.  If,  therefore,  on  adding  hydrochloric 
acid  or  a  soluble  chloride  to  a  solution,  a  precipitate  is 
formed,  the  conclusion  is  generally  justified  that  one  or 
more  of  the  three  metals — silver,  lead,  or  mercury — is 
present.  By  taking  into  account  the  differences  between 
these  chlorides,  it  is  not  difficult  to  decide  of  which  of 
them  a  precipitate  consists. 

Oxides. — These  occur  very  generally  in  nature,  and  are 
among  the  most  common  ores  of  some  of  the  important 
metals.  The  oxides  of  iron,  tin,  manganese,  etc.,  are  all 
found  in  nature.  They  can  be  made  by  oxidizing  the 
metals,  by  heating  nitrates  and  carbonates,  and  by  heating 
hydroxides. 

EXAMPLES. — When  magnesium  is  burned  (see  Experi- 
ment 14)  it  is  converted  into  magnesium  oxide: 

Mg  +  0  =  MgO. 


HYDROXIDES.  287 

When  lead  nitrate  is  heated  it  gives  off  oxygen  and  an 
oxide  of  nitrogen  and  leaves  behind  lead  oxide: 

Pb(N03)2  =  PbO  +  2N02  +  0. 

When  calcium  carbonate  is  heated  it  gives  off  carbon 
dioxide  and  leaves  behind  calcium  oxide,  CaO  : 

CaC03  =  CaO  -f  C02. 

Hydroxides.  —  The  hydroxides  are  formed  by  treating 
oxides  with  water,  and  by  decomposing  salts  by  adding 
soluble  hydroxides. 

EXAMPLES.  —  When  calcium  oxide  or  lime  is  treated  with 
water  it  is  converted  into  the  hydroxide,  Ca(OH)2,  or 
slaked  lime. 

EXPERIMENT  131.—  To  some  pieces  of  freshly-burned  lime  add 
enough  cold  water  to  cover  it.  The  action  which  takes  place  is 
represented  by  the  equation 

CaO  +  H2O  =  Ca(OH)2. 

The  process  is  known  as  slaking.  [What  evidence  have  you  that 
heat  is  evolved  in  the  reaction,  and  that  the  substance  obtained 
is  not  calcium  oxide  ?] 

Most  of  the  hydroxides  of  the  metals  are  insoluble  in 
water.  If  a  soluble  hydroxide  is  added  to  a  solution  con- 
taining a  metal  whose  hydroxide  is  insoluble,  the  latter  is 
precipitated.  Thus,  if  a  solution  of  sodium  hydroxide  is 
added  to  a  solution  of  a  magnesium  salt,  magnesium 
hydroxide  is  precipitated: 


MgS04  +  2NaOH  =  Na2S04  +  Mg(OH)2. 

EXPERIMENT  182.  —  To  a  small  quantity  of  a  dilute  solution  of 
magnesium  sulphate  add  a  dilute  solution  of  caustic  soda.  The 
white  precipitate  is  magnesium  hydroxide.  [Would  you  expect 
this  precipitate  to  be  soluble  in  sulphuric  acid  ?  in  hydrochloric 
acid  ?  in  nitric  acid  ?J  The  answers  follow  from  these  considera- 


288  INTRODUCTION   TO   CHEMISTRY. 

tions :  When  acids  act  upon  hydroxides,  salts  are  formed  ;  mag- 
nesium sulphate  is  soluble,  as  is  shown  by  the  fact  that  we 
started  with  a  solution  of  this  salt  ;  the  only  insoluble  chlorides 
are  those  of  silver,  lead,  and  mercury  ;  all  nitrates  are  soluble. 

When  a  solution  of  an  iron  salt  is  treated  with  sodium 
hydroxide  a  precipitate  of  iron  hydroxide  is  formed : 

FeCl3  +  3NaOH  =  Fe03U3  +  SNaCl. 

EXPERIMENT  133.— To  a  dilute  solution  of  that  chloride  of 
iron  which  is  known  as  ferric  chloride  add  caustic  soda.  The 
reddish  precipitate  formed  is  ferric  hydroxide.  [From  the  gen- 
eral statements  made  above,  would  you  expect  this  precipitate  to 
be  soluble  in  sulphuric  acid?  in  hydrochloric  acid?  in  nitric 
acid  ?  Try  each.] 

Only  the  hydroxides  of  the  members  of  the  potassium 
family  and  of  the  calcium  family  are  soluble  in  water. 
The  hydroxides  of  sodium  and  potassium  are  called 
alkalies.  The  solution  of  ammonia  in  water  acts  like  a 
soluble  hydroxide  and  probably  contains  the  ions  of  am- 
monium hydroxide,  NH4OH,  formed  by  the  action  of 
water  on  ammonia: 

NH3  +  H20  =  NH4OH. 

When  any  one  of  the  soluble  hydroxides  is  added  to  a 
salt  containing  any  metal  that  does  not  belong  to  the 
potassium  or  calcium  family,  an  insoluble  compound  is 
thrown  down. 

[Test  this  by  trying  such  salts  as  may  be  available. 
Note  the  results  in  each  case.  Is  an  insoluble  compound 
formed  ?  What  is  its  general  appearance  ?] 

Decomposition   of  Salts  by  Acids  and  by  Bases. — The 

decomposition  of  salts  by  the  addition  of  hydroxides  is  in 
some  respects  analogous  to  the  decomposition  of  salts  by 
the  addition  of  strong  acids. 


DECOMPOSITION  Of-   S/ILTS  BY  ACIDS  AND  BASES.  289 

When  an  acid  is  added  to  a  salt  there  are  three  cases 
which  may  present  themselves: 

1.  The  acid  from  which  the  salt  is  derived  may  be  vola- 
tile or  may  break  down,  yielding  a  volatile  product. 

In  this  case  decomposition  takes  place,  and  the  volatile 
acid  is  given  off.  This  is  illustrated  by  the  liberation  of 
hydrochloric  and  nitric  acids  from  chlorides  and  nitrates 
by  the  addition  of  sulphuric  acid,  and  of  carbon  dioxide 
from  carbonates  by  the  addition  of  other  acids. 

[Write  the  equations  representing  the  action  which 
takes  place  when  sulphuric  acid  acts  upon  potassium 
chloride,  calcium  chloride,  sodium  nitrate,  calcium  nitrate ; 
when  hydrochloric  acid  acts  upon  sodium  carbonate,  cal- 
cium carbonate.] 

2.  The  acid  from  which  the  salt  is  derived  may  be  in- 
soluble or  difficultly  soluble  in  water,  and  not  volatile. 

In  this  case,  if  the  salt  is  in  solution,  decomposition 
takes  place,  and  the  insoluble  or  difficultly  soluble  acid  is 
precipitated.  This  is  illustrated  by  the  liberation  of  boric 
acid  from  borax  by  the  addition  of  sulphuric  acid ;  and  by 
the  liberation  of  silicic  acid  by  the  addition  of  hydrochloric 
or  sulphuric  acid  to  a  soluble  silicate. 

3.  The  acid  from  which  the  salt  is  derived  may  be  solu- 
ble and  not  volatile  under  the  existing  conditions. 

In  this  case,  if  the  substances  are  in  solution,  apparently 
no  change  takes  place.  Thus,  when  nitric  acid  is  added 
to  sodium  chloride  in  solution  no  striking  change  takes 
place,'  no  gas  is  given  off,  no  precipitate  is  formed.  It  is 
extremely  difficult  to  determine  what  does  take  place  under 
these  circumstances.  A  study  of  such  cases  as  this  is  of 
great  importance  to  chemistry,  but  cannot  be  undertaken 
at  this  stage. 

Now,  to  return  to  the  action  of  hydroxides  upon  salts; 
when  a  soluble  base  acts  upon  a  salt,  three  cases  may 
present  themselves : 


290  INTRODUCTION   TO  CHEMISTRY. 

1.  The  base  from  which  the  salt  is  derived  may  be  vola- 
tile or  may  break  down,  yielding  a  volatile  product. 

In  this  case  decomposition  takes  place  and  the  volatile 
base  is  given  off.  This  is  not  a  common  case  except  among 
the  compounds  of  carbon.  The  one  illustration  which  we 
hfive  had  is  the  decomposition  of  ammonium  salts  by  cal- 
cium hydroxide  and  by  sodium  hydroxide. 

[Write  the  equations  representing  the  action  in  both 
cases.  In  what  does  the  analogy  between  the  decomposi- 
tion of  ammonium  salts  by  bases  and  of  carbonates  by  acids 
consist  ?] 

2.  The  hydroxide  or  base  from  which  the  salt  is  derived 
may  be  insoluble  or  difficultly  soluble  in  water,  and  not 
volatile. 

In  this  case,  if  both  the  salt  and  the  base  are  in  solution, 
decomposition  takes  place,  and  the  insoluble  or  difficultly 
soluble  hydroxide  or  base  is  precipitated.  This  has  already 
been  illustrated. 

3.  The  base  from  which  the  salt  is  derived  may  be  solu- 
ble and  not  volatile. 

In  this  case  there  is  no  direct  evidence  of  change. 
Thus,  when  sodium  hydroxide  is  added  to  potassium 
nitrate,  nothing  is  seen  except  a  clear  solution.  To  deter- 
mine what  takes  place  is  a  difficult  matter.* 

*  Here  a  word  of  warning  to  students.  Do  not  forget  that  when- 
ever a  precipitate  is  formed  there  is  something  in  the  solution  which 
is  just  as  important  as  the  precipitate.  Accustom  yourselves  to  re- 
gard every  case  of  chemical  action  as  a  whole.  The  statement  that 
a  precipitate  is  formed  when  sodium  hydroxide  is  added  to  a  solution 
of  an  iron  salt  is  a  very  imperfect  description  of  the  chemical  change 
that  takes  place.  Precipitates  have  come  to  be  regarded  in  a  false 
light,  in  consequence  of  the  contsant  use  made  of  them  for  purposes 
of  analysis.  It  must  be  remembered  that  analysis  is  not  chemistry, 
though  it  is  essential  to  the  study  of  chemistry  and  is  an  important 
application  of  the  science.  The  art  of  analysis  is  founded  upon  a 
knowledge  of  the  science  of  chemistry. 


SULPHIDES.  291 

Sulphides.  —  Many  sulphides  are  found  in  nature.  They 
are  made  by  heating  metals  with  sulphur;  by  treating 
solutions  of  salts  with  hydrogen  sulphide  or  soluble  sul- 
phides. 

EXAMPLES.  —  Among  the  common  natural  sulphides  are 
iron  pyrites,  FeS2;  lead  sulphide,  or  galenite,  PbS;  copper 
pyrites,  FeCuS2.  [Examine  several  specimens  of  each, 
and  note  their  general  properties.] 

When  copper  or  iron  is  heated  with  sulphur  the  corre- 
sponding sulphides  are  formed.  (See  Experiments  10  and 
112.)  [For  what  purpose  were  these  experiments  per- 
formed ?] 

When  hydrogen  sulphide  is  passed  through  a  solution 
containing  a  metal  whose  sulphide  is  insoluble,  the  sulphide 
is  precipitated.  This  has  been  illustrated  by  passing  the 
gas  through  solutions  of  lead  nitrate,  zinc  sulphate,  and 
arsenic  trioxide.  The  reactions  are  : 


Pb(N03)2  +  H2S  =  PbS 
ZnS04  +  H2S  =  ZnS  +  H2S04; 
As203  +  3H2S  =  As2S3  +  3H20. 

[What  differences  were  observed  in  these  three  cases  ? 
Repeat  the  experiments.] 

When  a  soluble  sulphide,  as  ammonium  sulphide  or 
sodium  sulphide,  is  added  to  a  solution  containing  a  metal 
whose  sulphide  is  insoluble,  the  insoluble  sulphide  is  thrown 
down. 

EXPERIMENT  134.  —  Add  ammonium  sulphide  successively  to 
dilute  solutions  of  an  iron  salt,  a  lead  salt,  a  copper  salt.  Note 
what  takes  place  in  each  case. 

Qualitative  Analysis,  —  The  sulphides  of  all  the  metals 
except  those  which  belong  to  the  potassium  and  calcium 
groups,  and  that  of  magnesium,  are  insoluble  in  water, 
Of  those  sulphides  which  are  insoluble  in  water,  some  are 


292  INTRODUCTION    TO   CHEMISTRY. 

insoluble  and  some  are  soluble  in  dilute  hydrochloric  acid. 
Further,  of  those  which  are  insoluble  in  dilute  hydrochloric 
acid,  some  are  soluble  and  some  are  insoluble  in  ammonium 
sulphide. 

These  facts  furnish  the  basis  of  the  method  commonly 
employed  in  analyzing  substances.  Suppose  we  have  a 
solution  containing  all  the  more  common  elements,  and  we 
wish  to  determine  what  is  in  it.  Let  us  suppose  that,  on 
adding  hydrochloric  acid  to  it,  a  precipitate  is  formed. 
This  precipitate  is  filtered  off,  and  the  solution  treated 
with  hydrogen  sulphide.  Those  metals  whose  sulphides 
are  insoluble  in  dilute  hydrochloric  acid  will  be  precipi- 
tated. Among  the  elements  which  may  be  contained  in 
this  precipitate  are  lead,  mercury,  copper,  tin,  arsenic. 
The  solution  from  which  the  precipitate  was  thrown  down 
may  still  contain  those  metals  whose  sulphides  are  soluble 
in  dilute  hydrochloric  acid.  If,  therefore,  we  filter  off  the 
precipitate  and  add  ammonium  sulphide  to  the  filtrate, 
the  metals  whose  sulphides  are  insoluble  in  neutral  or 
alkaline  solutions  will  be  thrown  down.  Among  these  are 
iron,  aluminium,  chromium,  manganese,  etc.  The  filtrate 
from  this  precipitate  may  contain  all  those  metals  whose 
sulphides  are  soluble  in  water.  By  means  of  other  reac- 
tions these  can  be  subdivided  into  groups.  In  the  ordi- 
nary method  of  analysis  we  have,  therefore,  several  groups 
of  elements  to  deal  with.  These  are : 

1.  The   hydrochloric-acid  group,    consisting    of    those 
metals  whose  chlorides  are  insoluble  in  water. 

2.  The   hydrogen-sulphide  group,    consisting   of  those 
metals  whose  sulphides  are  insoluble  in  dilute  hydrochloric 
acid. 

3.  The  ammonium- sulphide,  group,  consisting  of   those 
metals  whose  sulphides  are  soluble  in  dilute  hydrochloric 
acid,  but  are  precipitated  by  ammonium  sulphide. 

4.  Elements  whose  sulphides  are  soluble  in  water. 


HYDROSULPHIDES.  293 

Each  of  these  groups  can  be  subdivided,  and  the  sub- 
groups again  subdivided,  until  positive  evidence  of  the 
presence  of  certain  metals  is  obtained. 

Hydrosulphides  are  formed  when  hydrogen  sulphide  is 
passed  into  a  solution  of  a  hydroxide  until  no  more  is  taken 
up. 

Potassium  hydrosulphide  is  formed  thus: 

KOH  +  H2S  =  KSH  +  H20. 
Ammonium  hydrosulphide  is  formed  thus: 
NH4OH  +  H2S  =  NHJSH  +  H20. 

Nitrates. — These  salts  are  formed  by  treating  metals  Vith 
nitric  acid;  by  treating  oxides  or  hydroxides  with  nitric 
acid,  and  in  general  by  treating  any  easily -decomposed  salt 
as  a  carbonate  with  nitric  acid. 

EXAMPLES. — When  nitric  acid  acts  upon  copper,  copper 
nitrate  is  formed.  [What  else  is  formed  ?  Give  an 
account  of  the  changes  which  take  place.  Write  the 
equation  representing  the  reaction.  ] 

The  simple  neutralization  of  nitric  acid  with  a  base  or 
hydroxide  has  been  illustrated  in  the  experiments  on  acids 
and  bases  (Experiment  61).  [Write  the  equations  repre- 
senting the  reactions  which  take  place  when  nitric  acid  is 
neutralized  with  potassium  hydroxide,  with  calcium  oxide, 
with  calcium  hydroxide.] 

All  nitrates  are  soluble  in  water,  and  all  are  decomposed 
by  heat.  [Try  the  solubility,  in  water,  of  such  nitrates  as 
may  be  available.  ] 

EXPERIMENT  135. — Heat  2  to  3  grams  potassium  nitrate  on 
charcoal  in  the  blowpipe  flame.  The  decomposition  with  evo- 
lution of  gas  is  called  deflagration.  Heat  some  copper  nitrate 
and  powdered  lead  nitrate.  Note  the  changes  which  take  place, 
The  compounds  left  behind  are  copper  oxide  and  lead  oxide. 


294  INTRODUCTION   TO  CHEMISTRY. 

Chlorates  are  made  from  potassium  chlorate,  which  is 
made  by  treating  a  strong  solution  of  caustic  potash  with 
chlorine.  [Explain  the  reaction.] 

Chlorates  are  soluble  in  water,  and  are  decomposed  by 
heat  with  evolution  of  oxygen.  [When  potassium  chlorate 
is  heated,  what  takes  place  in  the  first  stage  of  the  opera- 
tion ?] 

Hypochlorites  are  formed  by  treating  some  of  the 
metallic  hydroxides  in  dilute  solution  with  chlorine.  This 
has  been  illustrated  in  the  formation  of  "bleachirig- 
powder,"  which  contains  calcium  hypochlorite.  [Explain 
what  takes  place  when  slaked  lime  is  treated  with  chlorine.] 

Hypochlorites  are  decomposed  by  heat. 

Sulphates. — Some  sulphates,  as  those  of  calcium  and 
barium,  are  found  in  nature,  the  former  being  known  as 
gypsum.  Sulphates  are  made  by  treating  metals  or 
metallic  hydroxides  or  oxides  with  sulphuric  acid;  by 
treating  easily-decomposed  salts,  as  carbonates,  with  sul- 
phuric acid ;  and  by  treating  a  solution  containing  a  metal 
whose  sulphate  is  insoluble,  with  sulphuric  acid  or  a 
soluble  sulphate. 

EXAMPLES. — Usually,  when  sulphuric  acid  acts  upon  a 
metal,  hydrogen  is  evolved  and  a  salt  is  formed.  This 
has  been  illustrated  in  the  preparation  of  hydrogen  by 
means  of  zinc  and  sulphuric  acid. 

EXPERIMENT  136. — Dissolve  some  iron  in  dilute  sulphuric  acid. 
When  the  action  is  over,  warm  and  filter  the  solution  and  allow 
it  to  crystallize.  [What  is  the  appearance  of  the  salt  ?  Does  it 
contain  water  of  crystallization  ?  Was  hydrogen  evolved  during 
the  action  of  the  acid  on  the  metal  ?]  Dry  some  of  the  salt,  and 
put  it  aside  for  further  use. 

EXPERIMENT  137.— Dissolve  some  copper  foil  in  concentrated 
sulphuric  acid.  [In  what  respect  does  the  action  in  this  case  differ 
from  that  in  the  hist  experiment  ?]  When  the  action  is  over,  and 
the  mass  has  cooled  down,  pour  it  into  three  or  four  times  its  vol- 


SULPHATES.  295 

ume  of  hot  water,  when  most  of  the  black  deposit  will  dissolve. 
Filter  tho  solution,  and  let  the  salt  deposit  in  the  form  of  crys- 
tals. [What  is  the  appearance  of  the  salt  ?  Does  it  contain 
water  of  crystallization  ?  What  does  the  salt  look  like  after  it 
has  been  heated  in  a  tube  ?]  Dry  some  of  it,  and  put  it  aside  for 
further  use.  [Write  the  equation  representing  the  action  which 
takes  place  when  copper  acts  upon  sulphuric  acid.] 

The  action  of  sulphuric  acid  on  metallic  hydroxides  has 
been  illustrated.  (See  page  124.) 

[Write  the  equation  representing  the  action  which  takes 
place  when  the  acid  acts  upon  sodium  hydroxide,  potas- 
sium hydroxide,  ammonium  hydroxide.  What  is  mono- 
sodium  sulphate  ?  What  is  neutral  sodium  sulphate  ?  Is 
there  any  difference  between  disodium  sulphate  and 
neutral  sodium  sulphate  ?] 

Most  sulphates  are  soluble  in  water.  The  sulphates  of 
barium,  strontium,  and  lead  are  insoluble  in  water,  and 
the  sulphate  of  calcium  is  difficultly  soluble.  Therefore, 
when  sulphuric  acid  is  added  to  a  solution  containing 
either  of  the  metals  barium,  strontium,  or  lead,  a  precipi- 
tate is  formed. 

EXPERIMENT  138. — Make  a  dilute  solution  of  barium  chloride, 
of  lead  nitrate,  of  strontium  nitrate.  To  a  small  quantity  of 
each  in  a  test-tube  add  a  little  sulphuric  acid.  In  each  case  a 
white  precipitate  is  formed.  [What  remains  in  solution  ?]  Make 
a  somewhat  concentrated  solution  of  calcium  chloride.  To  this 
add  some  sulphuric  acid.  A  precipitate  is  formed.  [What  is  in 
solution?]  Add  more  water,  and  see  whether  this  precipitate 
will  dissolve.  The  formulas  of  the  salts  used  in  the  experiments 
are  barium  chloride,  BaCla  ;  lead  nitrate,  Pb(NO8)2 ;  strontium 
nitrate,  Sr(NOs)s,  [Write  the  equations  expressing  the  reactions.] 
If  to  the  solutions  of  the  salts  any  soluble  sulphate  is  added  in- 
stead of  sulphuric  acid,  the  same  insoluble  sulphates  will  be 
formed.  The  sulphates  of  iron,  copper,  sodium,  and  potassium 
are  among  the  soluble  sulphates.  Make  dilute  solutions  of  small 
quantities  of  each  of  these,  and  add  them  successively  to  the  so- 
lutions of  barium  chloride,  lead  nitrate,  and  strontium  nitrate. 


296  INTRODUCTION    TO  CHEMISTRY. 

The  formula  of  iron  sulphate  is  FeS04 ;  of  copper  sulphate, 
CuSO4 ;  of  sodium  sulphate,  Na3SO4 ;  and  of  potassium  sulphate, 
K3SO4.  Write  the  equations  representing  the  reactions  which 
take  place  in  the  above  experiments.  It  need  hardly  be  explained 
that  the  action  consists  in  an  exchange  of  places  on  the  part  of 
the  metals.  Thus,  when  the  soluble  salt,  iron  sulphate,  FeSO4  , 
is  brought  together  with  the  soluble  salt,  barium  chloride,  BaCU  , 
the  insoluble  salt,  barium  sulphate,  BaSO4 ,  and  the  soluble  salt, 
iron  chloride,  FeCU ,  are  formed  : 

FeSO4  +  BaCU  =  Fe013  +  BaS04. 

When  heated  with  charcoal  in  the  reducing  flame  of  the 
blowpipe,  sulphates  are  reduced  to  sulphides: 

K^O,  +  40  =  K2S  +  4CO,     or 
K2S04  +  2C  =  K2S  +  2C02. 

EXPERIMENT  139.— Mix  and  moisten  a  little  sodium  sulphate  and 
finely-powdered  charcoal.  Heat  the  mixture  for  some  time  in 
the  reducing  flame.  After  cooling  scrape  off  the  salt,  dissolve  it 
in  a  few  cubic  centimetres  of  water,  and  filter  through  a  small 
filter.  If  the  change  to  the  sulphide  has  taken  place,  sodium  sul- 
phide, NaaS,  is  in  solution.  A  soluble  sulphide  when  added  to  a 
solution  containing  copper  gives  a  black  precipitate  of  copper 
sulphide.  Try  this  ;  also  try  the  action  of  a  drop  of  the  solution 
of  sulphide  on  a  bright  silver  coin. 

Sulphites  are  made  from  sodium  or  potassium  sulphite, 
which  are  made  by  treating  sodium  or  potassium  hydroxide 
in  solution  with  sulphur  dioxide : 

2NaOH  +  SO,  =  Na2S03  +  H20. 

All  sulphites  are  decomposed  by  the  common  acids,  sul- 
phur dioxide  being  given  off: 

Na2S03  +  H,S04  =-  Na,S04  +  H20  -f  S02. 

Carbonates. — Many  carbonates  are  found  in  nature, 
some  of  them  in  great  abundance,  and  widely  distributed. 
The  principal  one  is  calcium  carbonate.  They  are  made 


CARBONATES.  297 

by  passing  carbon  dioxide  into  solutions  of  hydroxides,  and 
by  adding  soluble  carbonates  to  solutions  of  salts  contain- 
ing metals  whose  carbonates  are  insoluble. 

EXAMPLES. — The  formation  of  potassium  carbonate  by 
the  treatment  of  potassium  hydroxide  with  carbon  dioxide 
has  already  been  illustrated.  (See  Experiment  93.) 

[Write  the  equation  representing  the  action.  Is  the 
salt  formed  in  this  case  soluble  or  insoluble  in  water  ?] 

The  formation  of  calcium  carbonate  by  passing  carbon 
dioxide  into  a  solution  of  calcium  hydroxide  (lime-water) 
has  been  illustrated  under  Carbon  Dioxide. 

[Describe  the  experiment.  Write  the  equation  repre- 
senting the  action  in  this  case.  Is  calcium  carbonate 
soluble  or  insoluble  in  water  ?  In  hydrochloric  acid,  in 
sulphuric  acid,  in  nitric  acid  ?  What  action  takes  place 
when  it  is  treated  with  each  of  these  acids  ?] 

EXPERIMENT  140. — The  formation  of  carbonates  by  the  addition 
of  soluble  carbonates  to  solutions  of  salts  of  metals  whose  carbon- 
ates are  insoluble  is  illustrated  by  the  following  experiments : 
Make  solutions  of  copper  sulphate,  iron  sulphate,  lead  nitrate, 
silver  nitrate,  calcium  chloride,  barium  chloride.  Add  to  each  a 
little  of  a  solution  of  a  soluble  carbonate,  as  sodium  carbonate, 
potassium  carbonate,  ammonium  carbonate.  Note  the  result  in 
each  case.  Filter  off  all  the  precipitates,  wash  them  thoroughly 
[Why  ?],  and  determine  whether  they  are  carbonates.  This  may 
he  done  by  treating  them  with  dilute  acids,  which  decompose 
them,  causing  an  evolution  of  carbon  dioxide,  which  can  be  de- 
tected by  passing  a  little  of  it  into  lime-water.  Write  all  the 
cquntions  representing  the  reactions  that  take  place  in  the  above 
experiments.  Here  again,  as  in  the  experiments  with  the  sul- 
phates, the  metals  exchange  places  : 

CuSO4  +  Na2C03  =  NaaSO4  +  CuCO3. 

[Is  copper  bivalent  or  univalent  if  the  formula  of  copper  sul- 
phate is  CuSCX  ?] 

All  carbonates  except  those  of  the  members  of  the  potas- 
sium farrr1/  are  insoluble,  and  are  decomposed  by  heat  into 


298  INTRODUCTION   TO   CHEMISTRY. 

carbon  dioxide  and  the  oxide  of  the  metal.  The  decom- 
position of  calcium  carbonate  into  lime  and  carbon  dioxide 
is  the  best-known  illustration  of  this  fact : 

CaC03  =  CaO  +  C0.2. 

Phosphates. — Calcium  phosphate  is  very  abundant  in 
nature,  and  a  few  other  phosphates  are  also  found.  The 
methods  of  making  phosphates  are  in  principle  the  same 
as  those  used  in  making  sulphates. 

The  phosphates  of  all  the  metals  except  the  members  of 
the  potassium  family  are  insoluble  in  water.  The  normal 
phosphates  [What  is  a  normal  phosphate  ?] ,  as  a  rule,  are 
not  changed  by  heat.  Those  phosphates  in  which  two 
thirds  of  the  hydrogen  is  replaced  by  metal — as,  for  exam- 
ple disodium  phosphate,  HNa2P04 — lose  water  when 
heated,  and  yield  pyrophosphates : 

2HNa2P04  =  Na4P207  +  H20. 

Sodium 
pyrophosphate. 

Those  phosphates  in  which  only  one  third  of  the  hy- 
drogen is  replaced  by  metal — as,  for  example,  monosodium 
phosphate,  H2NaP04 — lose  water  when  heated,  and  yield 
metaphosphates : 

H,NaP04  =  NaPO,  +  H20. 

Sodium 
metaphosphate. 

Neither  the  pyrophosphates  nor  the  metaphosphates  are 
changed  by  heat. 

Silicates. — The  extensive  occurrence  of  silicates  in  nature 
has  been  spoken  of.  Those  which  are  most  abundant  are 
the  feldspars  and  their  decomposition-products.  The 
principal  feldspar  is  a  complex  silicate  of  aluminium  and 


SILICATES.  299 

potassium,  of  the  formula   KAlSi308,  derived  from  the 
polysilicic  acid  H4Si308  [What  is  a  polysilicic  acid  ?] : 

3H,SiOs  =  H4Sis08  +  H,0. 

Silicates  can  be  made  by  heating  together  at  a  high 
temperature  silicon  dioxide,  in  the  form  of  fine  sand,  and 
bases. 

EXPERIMENT  141. — Heat  a  mixture  of  potassium  and  sodium 
carbonates  in  a  platinum  crucible  in  the  flame  of  the  blast-lamp  * 
until  the  mass  is  thoroughly  melted.  Add  sand  slowly  to  the 
fused  mass.  Pour  the  molten  mass  out  on  a  stone,  and  when 
cooled  break  it  up  and  treat  it  with  a  little  hot  water.  A  mix- 
ture of  potassium  and  sodium  silicates  passes  into  solution  : 

]STa2CO3  +  SiO2  =  NaaSiO3  +  CO2. 

Some  silicates  are  decomposed  by  the  ordinary  acids, 
such  as  sulphuric  and  nitric  acids,  the  silicic  acid  separat- 
ing as  a  difficultly  soluble  substance,  which  loses  water  and 
becomes  insoluble. 

EXPERIMENT  142.— Treat  a  little  of  the  solution  containing 
sodium  and  potassium  silicates,  prepared  in  the  last  experiment, 
with  a  little  sulphuric  or  hydrochloric  acid.  A  gelatinous  sub- 
stance will  be  precipitated.  This  is  silicic  acid.  Some  of  the  acid 
remains  in  solution  : 

NaaSi08  +  HaSO4  =  NaaS04  +  HaSiO3. 

By  evaporating  the  solution  to  dryness  and  heating  for  a  time 
on  the  water-bath,  all  the  silicic  acid  is  converted  into  silicon 
dioxide,  which  is  entirely  insoluble. 

Many  silicates  that  are  not  acted  upon  by  strong  acids 
are  decomposed  when  fused  with  sodium  or  potassium 
carbonate. 

Silicates  which  are  not  decomposed  in  either  of  the  ways 
mentioned  yield  to  hydrofluoric  acid.  The  action  consists 

*  This  is  a  large  blowpipe  worked  by  a  foot-bellows. 


300  INTRODUCTION   TO   CHEMISTRY. 

in  the  formation  of  the  gas,  silicon  tetrafluoride,  SiF4,  and 
the  fluorides  of  the  metals  present.  Thus,  the  reaction  ip 
the  case  of  feldspar  takes  place  according  to  the  equation 

KAlSis08  +  16HF  =  KF  +  AIF3  +  3SiF4  +  8H20. 

The  silicon  fluoride  is  given  of?  and  the  fluorides  of  the 
metals  are  soluble  in  water.  Hence  hydrofluoric  acid  dis- 
solves the  silicate.  [Is  this  use  of  the  word  dissolve? 
strictly  correct  ?] 

Keactions  in  Solution  are  Reactions  of  Ions. — While  in 
the  account  given  in  this  chapter  of  the  methods  of  making 
the  compounds  of  the  metals,  the  equations  used  have 
represented  the  compounds  as  acting  upon  one  another,  it 
is  clear  from  what  has  already  been  said  (see  page  126)  in 
regard  to  reactions  that  take  place  in  solution,  in  water 
at  all  events,  that  we  can  go  a  step  farther  in  expressing 
what  takes  place  in  these  reactions.  The  reactions  are 
believed  to  take  place  between  the  ions  that  are  formed 
when  the  substances  pass  into  solution.  Thus,  when 
hydrochloric  acid  dissolved  in  water  acts  upon  silver  nitrate 
dissolved  in  water  the  equation 

AgN03  +  II  Cl  =  AgCl  +  HN03 , 

while  telling  the  truth,  does  not  tell  the  whole  truth  as  the 
matter  is  now  understood.  For  in  the  solution  of  hydro- 
chloric acid  the  ions  H  and  Cl  are  present;  and,  in  the 
solution  of  silver  nitrate,  the  ions  Ag  and  N03.  Conse- 
quently, reaction  must  take  place  between  these.  It  is 
expressed  thus : 

H  +  Cl  +  Ag  +  NO,  =  H  +  N03  +  AgCl. 

The  substance  represented  by  the  formula  AgCl,  silver 
chloride,  is  insoluble  in  water,  and  is  therefore  removed 
from  the  field  of  action,  while  the  ions  II  and  N03  remain, 
forming  what  is  usually  called  a  solution  of  nitric  acid. 


REACTIONS  IN  SOLUTION.  301 

Bearing  in  mind  the  fact  that  acids,  in  general,  dis- 
sociate in  solution  into  hydrogen  ions  and  into  other  ions 
the  composition  of  which  depends  upon  the  composition  of 
the  acid;  that  bases  dissociate  into  hydroxyl  ions  and, 
generally,  metallic  ions;  and  that  salts  dissociate  into 
metallic  ions  and  the  ions  which  in  acids  are  in  com- 
bination with  hydrogen,  there  is  no  difficulty  in  translat- 
ing an  ordinary  chemical  equation  into  an  ionic  equation. 


CHAPTER   XX. 

THE     POTASSIUM     GROUP:     LITHIUM,    SODIUM,    PO- 
TASSIUM,  CAESIUM,   RUBIDIUM,   (AMMONIUM). 

General. — The  most  widely-distributed  and  hence  best- 
known  members  of  this  group  are  sodium  and  potassium. 
The  hypothetical  metal  ammonium  is  included  in  the 
group  because  the  salts  formed  by  ammonia,  in  which  this 
hypothetical  metal  is  regarded  as  present,  very  closely 
resemble  the  salts  of  potassium  and  sodium.  The  mem- 
bers of  the  group  are  generally  called  the  metals  of  the 
alkalies,  as  the  two  best-known  members  are  obtained  from 
the  alkalies,  caustic  potash  and  caustic  soda,  or  potassium 
and  sodium  hydroxides. 

Potassium,  K  (At.  Wt.  39.15). — This  element  is  a  con- 
stituent of  many  minerals,  particularly  of  feldspar,  which, 
as  already  explained,  is  a  complex  silicate  of  aluminium 
and  potassium.  It  is  found  also  in  combination  with 
chlorine  as  sylvite;  with  sulphuric  acid  and  aluminium, 
as  alum ;  with  nitric  acid,  as  saltpetre  or  potassium  nitrate ; 
and  in  other  forms.  The  natural  decomposition  of  min- 
erals .  containing  potassium  gives  rise  to  the  presence  of 
this  metal,  in  various  forms  of  combination,  everywhere 
in  the  soil.  It  is  taken  up  by  plants;  and  when  vegetable 
material  is  burned  the  potassium  remains  behind,  chiefly 
as  potassium  carbonate.  When  wood-ash  is  treated  with 

302 


POTASSIUM.  3°3 

water  the  potassium  carbonate  is  dissolved,  and  it  is  ob- 
tained in  an  impure  state  by  evaporating  the  solution. 
The  substance  thus  obtained  is  called  potash. 

EXPERIMENT  143. — If  convenient  treat  two  or  three  litres  of 
wood-ashes  with  water.  Filter  off  the  solution,  and  examine  it 
by  means  of  red  litmus-paper.  The  color  of  the  paper  is  changed 
to  blue.  Plainly  the  solution  is  alkaline.  Examine  some  potas- 
sium carbonate.  [Does  its  solution  act  in  the  same  way  ?] 
Evaporate  the  solution  to  dryness.  Collect  the  dry  residue  and 
treat  it  with  dilute  hydrochloric  acid.  [Is  a  gas  given  off  ?  Is  it 
carbon  dioxide  ?] 

Preparation. — The  metal  was  first  prepared  by  Sir 
Humphry  Davy,  in  the  year  1807,  by  the  action  of  a 
powerful  electric  current  on  potassium  hydroxide.  It  is 
now  manufactured  by  the  action  of  an  electric  current  on 
potassium  hydroxide,  cyanide,  or  chloride. 

Properties. — It  is  a  light  substance,  which  floats  on 
water.  [Have  you  had  evidence  of  this  ?]  Its  freshly-cut 
surface  has  a  bright  metallic  lustre,  almost  white;  it  acts 
upon  water  with  great  energy,  causing  the  evolution  of 
hydrogen,  which  burns,  and  the  formation  of  potassium 
hydroxide.  This  reaction  has  already  been  treated  of  in 
connection  with  hydrogen.  [Turn  back  to  the  experiment 
(Experiment  27)  and  perform  it  again.  It  will  now 
appear  much  clearer.]  In  consequence  of  its  action  on 
water,  potassium  cannot  be  kept  in  the  air.  It  is  kept 
under  some  oil  upon  which  it  does  not  act,  as  petroleum. 

Compounds  of  Potassium.  —  The  chief  compounds  of 
potassium  with  which  we  meet  are  the  iodide,  KI,  which 
is  extensively  used  in  medicine  and  in  photography;  the 
hydroxide,  or  caustic  potash,  KOH,  which  finds  extensive 
use  in  laboratories;  the  nitrate,  or  saltpetre,  KN03,  used 
in  the  manufacture  of  gunpowder;  the  chlorate,  KC103, 


3°4  INTRODUCTION   TO   CHEMISTRY. 

used  in  the  preparation  of  oxygen  and  in  medicine;  and 
the  carbonate,  K2C03. 

The  methods  used  in  preparing  some  of  these  compounds 
are  interesting,  as  illustrating  the  applications  of  the  prin- 
ciples of  chemistry. 

Potassium  Iodide,  KI,  is  made  by  treating  caustic  potash 
with  iodine  until  the  solution  begins  to  show  a  permanent 
yellow  color,  which  is  an  indication  that  no  more  iodine 
will  be  taken  up.  The  action  is  the  same  as  that  which 
takes  place  when  chlorine  acts  upon  warm  concentrated 
caustic  potash.  Both  the  iodide  and  iodate  are  formed : 

6KOH  +  61  =  5KI  -f  KI03  +  3H20. 

By  evaporating  off  all  the  water  and  heating  the  residue, 
the  iodate  is  decomposed  into  the  iodide  and  oxygen. 

EXPERIMENT  144. — Examine  a  bottle  of  crystallized  potassium 
iodide.  Taste  a  little.  Dissolve  some  in  water.  Add  some 
iodine  to  this  solution.  [Does  the  iodine  dissolve  ?]  Heat  a  little. 
[Does  it  contain  water  of  crystallization  ?]  Treat  a  crystal  or  two 
with  a  few  drops  of  concentrated  sulphuric  acid.  [What  takes 
place  ?  To  what  is  the  appearance  of  violet  vapors  due  ?  How 
many  gases  are  given  off  ?  (See  Experiment  107.)] 

Potassium  Hydroxide,  KOH. — This  well-known  sub- 
stance, commonly  called  caustic  potash,  is  prepared  by  the 
action  of  an  electric  current  on  a  concentrated  solution  of 
potassium  chloride: 

2KC1  +  2H20  =  2KOH  +  H2  +  C12. 

It  can  also  be  made  by  treating  potassium  carbonate  with 
calcium  hydroxide  in  a  silver  or  iron  vessel. 

EXPERIMENT  145.— Dissolve  50  grams  potassium  carbonate  in 
500  to  600  cc.  water.  Heat  to  boiling  in  an  iron  or  silver  vessel, 
and  gradually  add  the  slaked  lime  obtained  from  25  to  30  grams 
of  good  quick-lime.  During  the  operation  the  mass  should  be 


POTASSIUM  NITRATE.  3° 5 

stirred  with  an  iron  spatula.  After  the  solution  is  cool,  draw  it 
off  by  means  of  a  siphon  into  a  bottle.  This  may  be  used  in 
experiments  in  which  caustic  potash  is  required. 

The  reaction  is  based  upon  the  fact  that  calcium  carbonate  is 
insoluble,  and  that  potassium  carbonate  and  calcium  hydroxide 
are  soluble  : 

K,CO3  4-  Ca(OH)3  =  CaCO3  +  2KOH. 

The  hydroxide  is  a  white  brittle  substanco.  In  contact 
with  the  air  it  deliquesces  [What  does  this  mean  ?]  and 
absorbs  carbon  dioxide.  It  is  a  very  strong  base.  [Ex- 
plain the  action  that  takes  place  when  potassium  hydroxide 
acts  upon  ammonium  chloride,  ]STH4C1;  copper  sulphate, 
CuS04;  and  magnesium  nitrate,  Mg(N03)2.] 

Potassium  Nitrate,  KN03. — This  salt  is  commonly  called 
saltpetre.  Its  occurrence  in  nature  has  already  been  spoken 
of  under  Nitric  Acid.  [What  are  the  conditions  which 
give  rise  to  its  formation  ?]  When  refuse  animal  matter 
is  left  to  undergo  decomposition  in  the  presence  of  bases, 
nitrates  are  always  the  end-products.  Advantage  is  taken 
of  this  fact  for  the  purpose  of  preparing  saltpetre  arti- 
ficially, the  process  being  carried  on  on  the  large  scale  in 
the  "saltpetre  plantations."  In  these,  refuse  animal 
matter  is  mixed  with  earthy  material,  wood-ashes,  etc., 
and  piled  up.  These  piles  are  moistened  with  the  liquid 
products  from  stables.  After  the  action  has  continued  for 
two  or  three  years  the  outer  crust  is  taken  off  and  extracted 
with  water.  The  solution  thus  obtained  contains,  besides 
potassium  nitrate,  calcium  and  magnesium  nitrates.  It  is 
treated  with  a  water-extract  of  wood-ashes  or  with  potas- 
sium carbonate,  by  which  the  calcium  and  the  magnesium 
are  thrown  down  as  carbonates.  Much  of  the  saltpetre 
which  is  in  the  market  is  made  from  Chili  saltpetre,  or 
sodium  nitrate,  by  treating  it  with  potassium  chloride: 

3  +  KC1  =  KN03  +  NaCl. 


3°6  INTRODUCTION   TO   CHEMISTRY. 

Potassium  nitrate  crystallizes  in  long  rhombic  prisms  of 

salty  taste. 

Uses  of  Potassium  Nitrate. — It  is  used  in  the  prepara- 
tion of  sulphuric  acid  [What  part  does  it  play  in  the 
preparation  of  sulphuric  acid  ?] ,  and  of  nitric  acid  [How 
is  nitric  acid  obtained  from  it  ?] .  Its  chief  use  is  in  the 
manufacture  of  gunpowder. 

Gunpowder. — The  value  of  gunpowder  is  due  to  the  fact 
that  it  explodes  readily,  the  explosion  being  a  chemical 
change  accompanied  by  a  sudden  evolution  of  gases. 
Gunpowder  is  made  of  a  mixture  of  saltpetre,  charcoal, 
and  sulphur.  When  heated,  the  saltpetre  gives  off  oxygen 
and  nitrogen;  the  oxygen  combines  with  the  charcoal, 
forming  carbon  dioxide  and  carbon  monoxide,  and  the 
sulphur  combines  with  the  potassium,  forming  potassium 
sulphide.  When  a  mixture  of  saltpetre  and  charcoal  is 
burned,  the  reaction  which  takes  place  is  this : 

2KN03  +  30  =  C02  +  CO  +  2N  +  K2C03. 

EXPERIMENT  146. — Mix  15  grams  potassium  nitrate  and  2.5 
grams  powdered  charcoal.  Set  fire  to  the  mass  in  an  iron  vessel. 

By  adding  the  necessary  quantity  of  sulphur  the  carbon 
dioxide,  which  would  otherwise  remain  in  combination 
with  the  potassium  as  potassium  carbonate,  is  given  off  and 
potassium  sulphide  formed : 

2KN03  +  30  +  S  =  3C02  +  2N  +  K2S. 

For  this  reaction  the  constituents  should  be  mixed  in  the 
proportions : 

Saltpetre 74.83 

Charcoal 13. 31 

Sulphur 11.86 


100.00 


POTASSIUM  CHLORATE.  3° 7 

[PROBLEM. — What  would  be  the  volume,  at  0°  and  under  760 
mm.  pressure,  of  the  gases  evolved  from  5  grams  of  gunpowder 
containing  the  constituents  in  exactly  the  proportions  given 
above  ?] 

This  is  approximately  the  composition  of  all  powder. 
When  gunpowder  explodes,  the  gases  formed  occupy  about 
280  times  the  volume  occupied  by  the  powder  itself. 

Potassium  Chlorate,  KC103. — The  reactions  by  which 
potassium  chlorate  is  formed  when  chlorine  acts  upon  a 
solution  of  potassium  hydroxide  have  been  discussed  (see 
pp.  115-116).  In  the  manufacture  of  the  chlorate  it  is 
found  advantageous  first  to  make  calcium  chlorate,  and 
then  to  treat  this  with  potassium  chloride,  when,  at  the 
proper  concentration,  potassium  chlorate  crystallizes. 
The  process  in  brief  consists  in  passing  chlorine  into  a 
solution  of  calcium  hydroxide  in  which  an  excess  of 
hydroxide  is  held  in  suspension.  The  first  action  leads  to 
the  formation  of  calcium  hypochlorite.  When  the  solution 
of  this  salt  is  boiled  it  is  decomposed,  yielding  the  chlorate 
and  chloride: 

3Ca(OCl)2  =  Ca(03Cl)2  +  2CaCl2. 

On  now  treating  the  solution  with  potassium  chloride 
the  following  reaction  takes  place : 

Ca(03Cl)2  +  2KC1  =  2KC103  +  CaCl2. 

Properties, — Potassium  chlorate  gives  up  oxygen  very 
easily  and  is  hence  a  good  oxidizing  agent.  It  dissolves  in 
water  at  the  ordinary  temperatures  to  the  extent  of  6  parts 
in  100  of  water. 

Uses. — The  chief  uses  of  potassium  chlorate  are  for  the 
preparation  of  oxygen,  and  in  the  manufacture  of  matches 
and  fireworks.  The  tips  of  Swedish  safety-matches  are 


INTRODUCTION    TO   CHEMISTRY. 

made  of  potassium  chlorate  and  antimony  sulphide.  The 
surface  upon  which  they  are  rubbed  to  ignite  them  con- 
tains red  phosphorus.  The  chlorate  is  extensively  used  in 
medicine,  particularly  as  a  gargle  for  sore  throat. 

Potassium  Cyanide,  KCN. — This  salt  is  made  by  heat- 
ing potassium  ferrocyanide  or  yellow  prussiate  of  potash, 
K4Fe(C.N")6 ,  with  potassium,  and  extracting  the  mass  with 
water.  It  is  a  violent  poison.  Most  of  the  potassium 
cyanide  found  in  the  market  is  made  by  heating  potassium 
ferrocyanide  with  sodium  and  therefore  contains  a  large 
percentage  of  sodium  cyanide. 

The  reaction  when  potassium  is  used  is  this: 

K4Fe(CN)6  +  2K  =  6KON  -f-  Fe. 
When  sodium  is  used  it  is  this: 

K4Fe(CN)6  -f  2Na  =  4KCN  +  SNaCN  -f  Fe. 

Potassium  Sulphate,  K2S04. — This  salt  occurs  in  com- 
bination with  others  in  nature,  particularly  in  the  mineral 
kainite,  which  has  the  composition  K2S04.MgS04.MgCl2 
-f-  6H20.  This  occurs  in  Stassfurt  and  in  Kalusz.  Potas- 
sium sulphate  is  used  in  medicine,  and  in  the  preparation 
of  ordinary  alum  and  of  potassium  carbonate. 

Sodium,  Na  (At.  Wt.  23.05). — Sodium  occurs  very 
widely  distributed  and  in  large  quantities,  principally  as 
sodium  chloride.  It  is  found  in  a  number  of  silicates,  and 
is  a  constituent  of  plants,  especially  of  those  which  grow 
in  the  neighborhood  of  the  sea-shore  and  in  the  sea.  Just 
as  the  ashes  of  inland  plants  are  rich  in  potassium  car- 
bonate, so  the  ashes  of  sea-plants  and  those  which  grow 
near  the  sea  are  rich  in  sodium  carbonate.  It  is  found 
everywhere  in  the  soil,  but  generally  in  small  quantity,  its 
presence. being  due  to  the  decomposition  of  minerals  con- 


SODIUM.  309 

taining  it,  such  as  soda  feldspar,  or  albite.  It  occurs  also 
as  sodium  nitrate,  and  in  large  quantity  in  Greenland  as 
cryolite,  Na3AlF6,  or  AlF3.3NaF. 

Preparation. — It  is  prepared  by  the  electrolysis  of  sodium 
hydroxide  or  of  sodium  chloride,  to  which  is  added  potas- 
sium chloride  and  strontium  chloride  in  order  to  lower  the 
melting-point. 

Properties. — Its  properties  are  very  similar  to  those  of 
p3tassium.  It  is  light,  floating  on  water;  it  has  a  bright 
metallic  lustre,  and  is  soft.  It  decomposes  water,  but  not 
as  actively  as  potassium. 

[Describe  what  takes  place  when  potassium  is  thrown 
upon  water  and  when  sodium  is  similarly  treated.  How 
is  the  difference  accounted  for  ?] 

Sodium  readily  unites  with  oxygen,  and  is  used  in  some 
chemical  processes  as  a  reducing  agent  [What  is  a  reduc- 
ing agent  ?],  as,  for  example,  in  the  preparation  of  silicon, 
magnesium,  and  aluminium.  A  compound  of  mercury 
and  sodium,  known  as  sodium  amalgam,  is  used  in  some 
metallurgical  operations  connected  with  the  extraction  of 
silver  and  gold  from  their  ores. 

Compounds  of  Sodium. — The  chief  compounds  of  sodium 
are  the  chloride,  NaCl;  the  hydroxide,  or  caustic  soda, 
NaOH;  the  nitrate,  or  Chili  saltpetre,  NaN03;  the  sul- 
phate, Na2S04;  the  thiosulphate,  Na2S203;  the  carbonate, 
Na2C03;  the  borate,  or  borax,  Na2B407;  the  phosphate, 
HNa2P04;  and  the  silicate,  Na2Si03. 

Sodium  Chloride,  NaCl. — This  is  the  substance  which  is 
known  as  salt,  or  common  salt.  It  occurs  very  widely  dis- 
tributed, and,  as  it  is  easily  soluble,  much  of  the  water 
which  enters  into  the  ocean  contains  some  of  it  in  solution. 
Sea-water  contains  from  2V  to  3  per  cent.  The  most  im- 


INTRODUCTION   TO  CHEMISTRY. 

portant  deposits  are  those  at  Wieliczka  in  Galicia,  at 
Stassfurt  and  Reichenhall  in  Germany,  and  at  Cheshire  in 
England.  Besides  these  there  are,  however,  many  other 
deposits  in  the  United  States,  in  Africa,  and  in  Asia.  In 
some  places  the  salt  is  taken  out  of  the  mines  in  solid  form; 
in  others,  water  is  allowed  to  flow  into  the  mines,  and  to 
remain  for  some  time  in  contact  with  the  salt.  The  solu- 
tion thus  formed  is  drawn  or  pumped  out  of  the  mine,  and 
evaporated  by  appropriate  methods.  In  hot  countries  salt 
is  obtained  by  the  evaporation  of  sea-water,  the  heat  of  the 
sun  being  used  for  the  purpose.  Large  shallow  cavities 
are  made  in  the  earth,  and  into  these  the  water  flows  at 
high  tide,  or  it  is  pumped  up  into  them. 

Properties. — Sodium  chloride  crystallizes  in  colorless 
and  transparent  cubes.  Sometimes  that  which  occurs  in 
nature  is  colored  blue.  In  hot  water  it  is  but  little  more 
soluble  than  in  cold  water.  In  crystallizing,  the  crystals 
enclose  water,  not  as  water  of  crystallization,  and  this  is 
given  off  when  the  crystals  are  heated,  the  action  being 
accompanied  by  a  crackling  sound.  This  is  known  as 
decrepitation. 

Uses. — Salt  is  used  as  the  starting-point  in  the  prepara- 
tion of  all  sodium  compounds  and  of  chlorine  and  hydro- 
chloric acid.  Salt  is  necessary  to  the  life  of  man  and 
many  other  animals. 

[How  are  chlorine  and  hydrochloric  acid  obtained  from 
it  ?  What  takes  place  when  a  solution  of  silver  nitrate  is 
added  to  a  solution  of  common  salt  ?  What  substances 
besides  silver  nitrate  act  in  the  same  way  ?] 

Sodium  Hydroxide,  NaOH. — This  is  commonly  called 
caustic  soda.  It  is  prepared  either  by  treating  metallic 
sodium  with  water,  or  by  the  electrolysis  of  concentrated 


COMPOUNDS   OF  SODIUM.  311 

solutions  of  sodium  chloride.  (See  Potassium  Hydrox- 
ide.) Its  properties  are  very  similar  to  those  of  caustic 
potash.  [Are  the  hydroxides  of  the  metals  mostly  soluble 
or  insoluble  substances  ?] 

Sodium  Nitrate,  NaN03. — This  compound  occurs  in 
large  quantity  in  southern  Peru,  on  the  border  of  Chili, 
and  is  known  as  Chili  saltpetre.  The  natural  salt  con- 
tains, besides  the  nitrate,  sodium  chloride,  sulphate,  and 
iodide.  Sodium  nitrate  is  very  similar  to  potassium 
nitrate,  but  it  cannot  be  used  in  place  of  the  more  expen- 
sive potassium  salt  in  the  manufacture  of  the  finer  grades 
of  gunpowder,  as  it  becomes  moist  in  the  air  and  does  not 
decompose  quickly  enough.  It  is  used  extensively  in  tho 
manufacture  of  nitric  acid,  and  also  for  the  purpose  of 
preparing  ordinary  saltpetre.  The  iodine  contained  in  it 
is  extracted  on  the  large  scale,  and  this  forms  an  impor- 
tant source  of  iodine. 

Sodium  Sulphate,  Na2S04  -j-  10H20. — The  common  name 
of  this  substance  is  Glauber's  salt.  It  is  made  on  the  large 
scale  by  the  action  of  sulphuric  acid  on  sodium  chloride : 

2NaCl  +  H2S04  =  Na2S04  +  2HC1; 

and  by  the  action  of  magnesium  sulphate  on  sodium 
chloride : 


MgS04  =  Na2S04 

The  salt  crystallizes  in  large  colorless  monoclinic  prisms, 
containing  10  molecules  of  water  of  crystallization, 
Na2S04  +  10H20.  It  loses  water  when  left  in  contact 
with  the  air.  [Is  it  efflorescent  or  deliquescent  ?] 

It  is  extensively  used  in  the  manufacture  of  glass. 

Sodium  Thiosulphate,  Na2S203  +  5H20.  —  This  is  the 
salt  commonly  called  hyposulphite  of  soda.  It  is  made  on 


312  INTRODUCTION   TO   CHEMISTRY. 

the  large  scale  by  treating  caustic  soda  with  sulphur,  and 
conducting  sulphur  dioxide  into  the  solution.  It  is  also 
made  by  adding  sulphur  to  a  boiling  solution  of  sodium 
sulphite : 

Na2S03  +  S  =  Na2S203. 

Its  chief  application  is  in  photography,  in  which  art  it  is 
used  for  the  purpose  of  dissolving  the  excess  of  silver  on 
the  plate  after  exposure. 

Sodium  Carbonate,  Na2CO,  -j-  10H20.—  This  salt,  com- 
monly called  soda,  is  one  of  the  most  important  of  manu- 
factured chemical  substances.  The  mere  mention  of  the 
fact  that  it  is  essential  to  the  manufacture  of  glass  and 
soap  will  serve  to  give  some  conception  of  its  importance. 
It  is  found  in  the  ashes  of  sea-plants,  just  as  potassium 
carbonate  is  found  in  the  ashes  of  those  plants  which  grow 
on  the  land.  We  are,  however,  not  dependent  on  sea- 
plants  for  our  supply,  as  two  methods  have  been  devised 
for  preparing  sodium  carbonate  from  sodium  chloride  with 
which  nature  provides  us  in  such  abundance.  As  these 
methods  are  interesting  applications  of  chemical  principles, 
H  will  be  well  to  consider  them  briefly. 

The  Le  Blanc  Process, — The  problem  to  be  solved  is  to 
convert  sodium  chloride,  NaCl,  into  sodium  carbonate, 
Na2C03.  *^The  process  devised  by  Le  Blanc  for  the  French 
government  during  the  Eevolution,  when  the  supply  had 
been  cut  off,  involves  four  reactions: 

1st,  The  sodium  chloride  is  converted  into  sodium  sul- 
phate by  treating  it  with  sulphuric  acid : 

2Na01  +  H2S04  =  Na2S04  +  2HC1. 

3d.  The  sodium  sulphate  thus  obtained  is  heated  with 
charcoal,  which  reduces  it  to  sodium  sulphide,  Na2S: 


THE  IE  BLANC  AND  SOLYAY  PROCESSES.          313 

£Ta2S04  +  40  =  Na,S  -f  400; 
20  =  NaS      2C0. 


3d.  The  sodium  sulphide  is  heated  with  calcium  car- 
bonate, when  sodium  carbonate  and  calcium  sulphide  are 
formed  : 

Na2S  +  CaC03  =  Na2C03  +  CaS. 

Calcium  sulphide  is  insoluble  in  water  containing  lime, 
so  that  by  treating  the  resulting  mass  with  water  the 
sodium  carbonate  is  separated  from  the  sulphide. 

In  practice  the  sodium  sulphate  is  mixed  with  coal  and 
calcium  carbonate,  and  the  mixture  heated.  The  coal 
reduces  the  sulphate  to  the  sulphide,  which  acts  upon  the 
calcium  carbonate,  forming  sodium  carbonate  and  calcium 
sulphide.  The  product  of  the  action  is  known  as  crude 
soda  or  Hack  ash.  In  order  to  purify  this  product,  it  is 
broken  into  pieces,  and  treated  with  water.  Soda  comes 
into  the  market  as  calcined  purified  soda,  which  contains 
no  water  of  crystallization,  and  as  crystallized  soda,  which 
has  the  composition  Na2C03  -f  10H20. 

This  process  is  now  only  in  use  in  England. 

The  Solvay  or  Ammonia  Process.  —  Another  and  cheaper 
process  is  the  so-called  ammonia-soda  process,  or  the  Solvay 
process.  This  depends  upon  the  fact  that  monosodium 
carbonate,  HNaC03  ,  is  comparatively  difficultly  sohible  in 
water.  If,  therefore,  monoammonium  carbonate,  or  acid 
ammonium  carbonate,  HNH4C03  ,  is  added  to  a  solution 
of  common  salt,  acid  sodium  carbonate,  HNaC03  ,  crystal- 
lizes out,  and  ammonium  chloride  remains  behind  in  the 
solution  : 

NaCl  +  HNH4C03  =  HNaC03  +  NH401. 

When  the  acid  carbonate  is  heated,  it  gives  off  carbon 
dioxide,  and  is  converted  into  the  normal  salt  thus: 

s  =  Na2003  +  H,0  +  C02. 


INTRODUCTION   TO  CHEMISTRY. 

The  carbon  dioxide  given  off  is  passed  into  ammonia 
and  thus  again  obtained  in  the  form  of  acid  ammonium 
carbonate : 

'NH8  +  H20  +  C02  =  HNH,C03. 

The  ammonium  chloride  obtained  in  the  first  reaction 
is  treated  with  lime  or  magnesia,  MgO,  and  the  ammonia 
set  free.  This  ammonia  is  again  used  in  the  preparation 
of  acid  ammonium  carbonate. 

The  larger  part  of  the  soda  supply  of  the  world  is  now 
furnished  by  the  Solvay  process. 

EXPERIMENT  147.— Make  a  saturated  solution  of  common  salt 
in  ordinary  ammonia- water  (about  50  cc.).  Pass  carbon  dioxide 
into  this  solution  until  no  more  is  absorbed,  the  delivery-tube 
being  as  in  Exp.  58.  Filter  off  the  precipitate,  and  dry  it  by 
spreading  it  upon  layers  of  filter-paper.  Heat  some  of  the  salt 
when  dry,  and  dote/mine  whether  the  gas  given  off  is  carbon 
dioxide  or  not.  JDFnen  gas  is  no  longer  given  off  by  heat,  let  the 
tube  cool  and  examine  the  residue.  [Is  it  a  carbonate  ?] 

Properties.  —  Sodium  carbonate  crystallizes  in  large 
monoclinic  prisms  with  10  molecules  of  water  of  crystal- 
lization. The  crystals  are  efflorescent. 

Monosodium  Carbonate,  Primary  Sodium  Carbonate, 
HNaC03. — This  salt  is  commonly  called  "bicarbonate  of 
soda."  It  is  easily  prepared  by  passing  carbon  dioxide 
over  the  ordinary  carbonate  dissolved  in  its  water  of 
crystallization : 

Na2C03  +  C02  +  H20  =  2HNaC03. 

When  heated  it  gives  up  carbon  dioxide  and  water,  and 
is  converted  into  the  normal  salt.  It  is  used  in  medicine, 
and  extensively  in  the  preparation  of  soda-water  and  other 
effervescent  drinks. 

Disodium  Phosphate,  HNa2P04  +  12H20.—  This  is  the 
common  form  of  sodium  phosphate.  It  is  formed  when 


SODIUM  BORATE.  3*5 

phosphoric  acid  is  treated  with  sodium  carbonate  until  the 
solution  begins  to  show  an  alkaline  reaction  with  red 
litmus.  It  is  a  remarkable  fact  that,  although  phosphoric 
acid  is  tribasic,  and  with  most  metals  forms  salts  that  arc 
derived  from  the  acid  by  replacement  of  all  the  three 
hydrogen  atoms,  as  Ag3P04,  Ca3(P04)2,  etc.,  with  sodium 
its  most  stable  salt  is  the  one  in  which  sodium  is  substi- 
tuted for  two  hydrogen  atoms.  A  salt  of  the  formula 
Na3P04  can  be  made,  but  it  has  an  alkaline  reaction,  and 
absorbs  carbon  dioxide  from  the  air,  being  converted  into 
sodium  carbonate  and  disodium  phosphate: 


2Na3P04  +  C02  +  H20  =  2HNa2P04  +  Na2C03. 

Sodium  Borate,  Na2B407  -f  10H20.—  This  salt  has  been 
referred  to  under  Boric  Acid.  It  is  commonly  called 
borax.  It  is  found  in  nature  in  several  lakes  in  Asia,  and 
in  this  country  in  Clear  Lake,  Nevada.  It  is  manufac- 
tured by  neutralizing  the  boric  acid  found  in  Tuscany. 

When  heated,  borax  puffs  up,  and  at  red  heat  melts, 
forming  a  transparent  colorless  liquid.  This  is  anhydrous 
borax,  Na2B407.  Molten  borax  has  the  power  to  dissolve 
metallic  oxides,  and  forms  colored  glasses  with  some  of 
them.  It  is  used  in  blowpipe  work  (see  Boric  Acid).  As 
it  dissolves  metallic  oxides,  it  is  used  in  the  process  of 
soldering,  as  it  is  necessary  to  have  bright,  untarnished 
metallic  surfaces  in  order  that  the  solder  shall  adhere 
firmly.  Borax  is  an  antiseptic;  that  is  to  say,  it  prevents 
the  decomposition  of  organic  substances.  It  is  used  ex- 
tensively in  the  manufacture  of  porcelain  and  in  glass- 
painting. 

Ammonium  Salts.  —  The  method  of  formation  of  the 
so-called  ammonium  salts  has  been  described  (see  Am- 
monia). These  salts  resemble  the  salts  of  potassium  and 
sodium  in  many  respects,  and  they  are  hence  described  in 


316  INTRODUCTION   TO   CHEMISTRY. 

the  same  connection.  The  chief  ones  are  the  chloride, 
NH4C1;  the  carbonate,  (NH4)2C03;  the  sulphide,  (NH4)2S; 
the  hydrosulphide,  (NH4)HS;  and  sodium- ammonium 
phosphate,  HNaNH4P04  +  4H20. 

Ammonium  Chloride,  NH4C1. — This  salt  is  commonly 
called  sal  ammoniac.  At  present  its  principal  source  is 
the  gas-works.  The  ammonia-water  of  the  works  is 
neutralized  with  hydrochloric  acid,  and  the  salt  obtained 
by  evaporation.  It  has  a  sharp,  salty  taste,  and  is  easily 
soluble  in  water.  When  heated  it  is  converted  into  vapor 
without  melting,  and  with  very  slight  decomposition;  and 
when  the  vapor  comes  in  contact  with  a  cold  surface,  it 
condenses  in  the  form  of  crystals.  This  process  of  vapor- 
izing and  condensing  a  solid  is  called  sublimation. 

EXPERIMENT  148. — On  a  piece  of  platinum  foil  or  porcelain  heat 
a  little  ammonium  chloride.  It  will  pass  off  and  form  a  dense 
white  cloud.  This  is  the  same  cloud  that  is  formed  by  bringing 
together  gaseous  ammonia  and  hydrochloric  acid.  All  ammo- 
nium salts  are  either  volatile  or  decompose  when  heated. 

[What  takes  place  when  ammonium  chloride  is  treated 
with  caustic  soda  ?  with  lime  ?  with  sulphuric  acid  ?] 

Ammonium  Sulphide,  (NHJ2S. — This  substance  is  ex- 
tensively used  in  chemical  analysis  for  the  purpose  of 
precipitating  those  sulphides  which  are  soluble  in  dilute 
hydrochloric  acid.  As  will  be  remembered,  in  analyzing 
a  mixture  of  substances  the  first  thing  usually  done  is  to 
add  hydrochloric  acid  to  the  solution.  This  precipitates 
silver,  lead,  and,  under  certain  conditions,  mercury.  This 
precipitate  having  been  filtered  off,  hydrogen  sulphide  is 
passed  through  the  filtrate,  when  those  metals  whose  sul- 
phides are  insoluble  in  dilute  hydrochloric  acid  are  thrown 
down.  The  precipitate  is  filtered  off  and  ammonium  sul- 
phide added  to  the  filtrate,  when  the  metals  whose 


AMMONIUM  SULPHIDE.  317 

sulphides  are  soluble  in  dilute  hydrochloric  acid  are  thrown 
down.  Among  these  are  iron,  cobalt,  nickel,  manganese, 
etc.  Any  other  soluble  sulphide  might  be  used,  but  the 
advantage  of  ammonium  sulphide  is  that  it  is  volatile,  and, 
hence,  by  evaporating  the  solution  and  heating,  it  can  be 
got  rid  of. 

Ammonium  sulphide  is  made  by  passing  hydrogen  sul- 
phide into  an  aqueous  solution  of  ammonia.  If  the  gas  is 
passed  in  until  the  solution  is  saturated,  the  product  is  the 
hydrosulphideHNH.S: 

HS  =  HNHS. 


If  only  half  this  quantity  of  the  gas  is  passed  in,  the 
product  is  the  sulphide  : 


H2S  = 

The  simplest  way  to  make  it  is  to  divide  a  quantity  of  a 
solution  of  ammonia  into  two  equal  parts.  Saturate  one 
half,  thus  forming  the  hydrosulphide,  and  add  the  other 
half,  when  this  reaction  takes  place  : 

HNH.S  +  NH,  =  (NH4)2S. 

The  product  is  a  colorless  liquid  of  a  disagreeable  odor. 
It  soon  changes  color,  becoming  yellow,  and  after  a  time 
a  yellow  deposit  is  formed  in  the  vessel  in  which  it  is  con- 
tained. This  change  of  color  is  due  to  the  action  of  the 
oxygen  of  the  air.  Some  of  the  sulphide  is  decomposed 
into  ammonia,  water,  and  sulphur: 

(NH4)2S  +  0  =  2NH3  4-  H20  +  S. 

The  sulphur  thus  set  free  combines  with  the  undecom- 
posed  ammonium  sulphide,  forming  the  compounds 
(NH4)2S2,  (NH4),S3,  etc.,  known  as  poly  sulphides.  When 
as  much  sulphur  as  possible  has  been  taken  up  in  this  way, 


INTRODUCTION   TO  CHEMISTRY. 

any  more  that  may  be  set  free  by  the  action  of  oxygen  is 
deposited. 

A  solution  containing  the  polysulphides  is  called  yelloiv 
ammonium  sulphide.  It  is  used  to  dissolve  the  sulphides 
of  arsenic,  antimony,  and  tin  in  analytical  operations. 
(See  description  of  method  of  analysis,  p.  292.) 

EXPERIMENT  149. — Saturate  25  cc.  strong  aqueous  amraon  ; 
with  hydrogen  sulphide.  Add  to  the  saturated  solution  25  cc.  <• 
the  same  ammonia. 

Ammonium  Hydrosulphide,  HNH4S. — As  stated  above, 
a  solution  of  this  substance  is  made  by  passing  hydrogen 
sulphide  into  a  solution  of  ammonia  until  no  more  is 
taken  up. 

Sodium-ammonium  Phosphate,  HNaNH4P04-{-4H20.— 

This  is  commonly  called  microcosmic  salt,  and  is  much 
used  in  the  laboratory  in  blowpipe  work.  Its  value,  in 
this  kind  of  work  depends  upon  the  fact  that  it  is  decom- 
posed by  heat,  yielding  sodium  metaphosphate : 

HNaNH4P04  =  NaP03  +  OT3  +  H20; 

and  the  metaphosphate  at  high  temperatures  combines 
with  the  metallic  oxides,  forming  double  phosphatei,  many 
of  which  are  colored. 

General  Characteristics  of  the  Metals  of  the  Alkalies.  — 
From  what  has  been  said,  it  will  be  seen  that  nearly  all 
the  compounds  of  these  metals  are  soluble  in  water.  Of 
those  mentioned  only  monosodium  carbonate  is  at  all 
difficultly  soluble.  There  are  a  few  insoluble  salts  of 
potassium,  those  which  are  chiefly  used  in  analytical 
operations  being  the  chloroplatinate,  K2PtCl6,  which  is 
formed  by  adding  a  solution  of  chlorplatinic  acid,  H2PtCl6, 
to  a  solution  containing  potassium  chloride : 

2KC1  +  H,PtCl6  =  K2Pt016  +  2HC1; 


ATOMIC   WEIGHTS   OF   THE  POTASSIUM  GROUP.    3*9 

and  the  fluosilicate,  K2SiF6,  which  is  formed  when  a  solu- 
tion of  fluosilicic  acid,  H2SiF6 ,  is  added  to  a  solution  con- 
taining a  salt  of  potassium. 

EXPERIMENT  150. — Add  chlorplatinic  acid  (commonly  called 
platinum  ohloride)  and  fluosilicic  acid  successively  to  strong  so- 
lutions of  potassium  chloride.  If  in  the  former  case  no  precipi- 
tate is  formed  add  a  little  alcohol  ;  potassium  chloroplatinate  is 
slightly  soluble  in  water,  but  is  insoluble  in  dilute  alcohol.  Po- 
tassium fluosilicate  is  precipitated  only  from  rather  concentrated 
solutions,  and  even  from  these,  as  a  rule,  only  after  standing  for 
a  while. 

Rare  Elements  of  this  Group. — The  elements  lithium, 
cesium,  and  rubidium  are  much  rarer  than  sodium  and 
potassium.  Lithium  is  found  in  a  form  of  mica  known 
as  lepidolite.  It  is  the  lightest  metal  known,  and  has  the 
smallest  atomic  weight,  viz.,  7.03. 

Relations  between  the  Atomic  Weights  of  the  Members 
of  this  Group. — The  relations  between  the  atomic  weights 
of  the  members  of  this  group  are  similar  to  those  already 
noticed  between  chlorine,  bromine,  and  iodine;  sulphur, 
selenium,  and  tellurium;  and  phosphorus,  arsenic,  and 
antimony.  Thus,  we  have  lithium,  7.03;  sodium,  23.05; 
and  potassium,  39.15.  The  atomic  weight  of  sodium, 
23.05,  is  nearly  the  mean  of  those  of  lithium,  7.03,  and 
potassium,  39.15: 

7.03  + 39.15  =  33()9 

z 

Similarly,  the  atomic  weight  of  rubidium,  85.4,  is  nearly 
the  mean  of  those  of  potassium  and  caesium,  133 : 

39.15  +  133 


2 


=  86.08. 


Flame  Reactions. — When  a  clean  piece  of  platinum  wire 
is  held  for  some  time  in  the  flame  of  the  Bunsen  burner, 


320  INTRODUCTION   TO  CHEMISTRY. 

it  then  imparts  no  color  to  the  flame.  If  now  a  small 
piece  of  sodium  carbonate  or  any  other  salt  of  sodium  is 
put  on  it,  it  colors  the  flame  intensely  yellow.  All  sodium 
compounds  have  this  power,  and  the  chemist  makes  use 
of  the  fact  for  the  purpose  of  detecting  the  presence  of 
sodium.  Similarly,  potassium  compounds  color  the  flame 
violet ;  lithium  compounds  color  the  flame  red ;  and  the 
other  metals  of  the  family  also  impart  characteristic  colors 
to  the  flame. 

EXPERIMENT  151.— Prepare  some  pieces  of  platinum  wire,  8  to 
10  cm.  long,  with  a  loop  on  the  end,  like  those  described  for 
blowpipe  work.  After  thoroughly  cleaning  them,  insert  one  in  a 
little  sodium  carbonate,  and  notice  the  color  it  gives  to  the  flame 
Try  another  with  potassium  carbonate,  and,  if  the  substances  are 
available,  others  with  a  lithium,  a  caesium,  and  a  rubidium  com- 
pound. 

The  Spectroscope. — While  it  is  an  easy  matter  to  recog- 
nize potassium  alone,  or  any  one  of  the  other  metals  of  this 
group  alone,  it  is  difficult  to  do  so  when  they  are  together 
in  the  same  compound.  For  example,  when  potassium 
and  sodium  are  together,  the  intense  yellow  caused  by  the 
sodium  completely  masks  the  more  delicate  violet  caused 
by  the  potassium,  so  that  the  latter  cannot  be  seen  with  the 
unaided  eye.  In  this  particular  case  the  difficulty  can  be 
overcome  by  letting  the  light  pass  through  a  blue  glass,  or 
a  thin  glass  vessel  filled  with  absolution  of  indigo.  The 
yellow  light  is  thus  cut  off,  while  the  violet  light  passes 
through  and  can  be  recognized.  A  more  general  method 
for  detecting  the  constituents  of  light  is  by  means  of  a 
prism.  Lights  of  different  colors, are  turned  out  of  their 
course  to  different  extents  when  passed  through  a  prism, 
as  is  seen  when  white  sunlight  is  passed  through  a  prism. 
A  narrow  beam  of  white  light  passing  in  emerges  as  a  band 
of  various  colors,  called  its  spectrum.  We  thus  see  that 
white  light  consists  of  different  colored  lights.  Similarly, 


THE  SPECTROSCOPE.  321 

we  can  determine  what  any  light  is  composed  of.  Every 
light  has  its  own  characteristic  spectrum.  The  light 
produced  by  burning  sodium,  or  by  introducing  a  sodium 
compound  in  a  colorless  flame,  has  a  spectrum  consisting 
of  a  narrow  yellow  band.  The  spectrum  of  potassium 
consists  essentially  of  two  bands,  one  red  and  one  violet. 
Further,  these  bands  always  occupy  definite  positions 
relatively  to  one  another,  so  that,  on  looking  through  a 
prism  at  the  light  caused  by  potassium  and  sodium,  the 
yellow  band  of  sodium  is  seen  in  its  position,  and  the  two 
potassium  bands  in  their  proper  positions. 

The  instrument  used  for  the  purpose  of  observing  the 
spectra  of  different  lights  is  called  the  spectroscope.  It 
consists  essentially  of  a  prism  and  two  tubes.  Through 
one  of  the  tubes  the  light  to  be  examined  is  allowed  to 
pass  so  as  to  strike  the  prism  properly.  The  light  emerges 
from  the  other  side  of  the  prism,  and  is  observed  through 
the  other  tube,  which  is  provided  with  lenses  for  the 
purpose  of  magnifying  the  spectrum.  By  means  of  the 
spectroscope  it  is  possible  to  detect  the  minutest  quanti- 
ties of  some  elements,  and,  since  it  was  devised,  several 
new  elements  have  been  discovered  through  its  aid,  as,  for 
example,  caesium,  rubidium,  thallium,  indium,  gallium, 
and  others.* 

*  For  an  account  of  the  spectroscope  and  its  uses  the  student  is 
advised  to  consult  some  work  on  physics.  The  principles  involved 
in  its  construction  are  physical  principles,  arid  cannot  properly  bo 
taken  up  in  detail  in  a  text-book  of  chemistry. 


CHAPTER   XXI. 

THE   CALCIUM   GROUP: 
CALCIUM,   BARIUM,   STRONTIUM,   GLUCINUM. 

General. — The  three  elements  calcium,  barium,  and 
strontium  resemble  one  another  very  closely.  Calcium  is 
much  more  abundant  than  either  of  the  other  members  of 
the  group,  while  strontium  is  the  least  abundant  of  the 
three.  For  the  present  it  will  be  best  to  confine  our 
attention  to  the  principal  member,  viz.,  calcium. 

Calcium,  Ca  (At.  Wt.  40). — This  element  occurs  very 
widely  distributed  in  nature,  and  in  enormous  quantities. 
It  is  found  principally  as  carbonate,  CaC03,  in  the  form 
of  limestone,  marble,  and  chalk;  as  sulphate,  CaS04,  in 
the  form  of  gypsum;  as  phosphate,  Ca3(POJ2,  in  phos- 
phorite and  apatite;  as  fluoride,  CaF2,  in  fluor-spar. 

The  element  is  made  by  heating  a  mixture  of  calcium 
oxide  and  carbon  in  an  electric  furnace. 

It  is  a  silver-white,  lustrous  substance,  which  in  moist 
air  becomes  covered  with  a  layer  of  hydroxide.  At  ordi- 
nary temperatures  it  decomposes  water  just  as  sodium  and 
potassium  do.  It  is  one  of  the  most  active  elements. 

Compounds  of  Calcium, — The  principal  compounds  of 
calcium  with  which  we  have  to  deal  are  the  chloride,  Ca012 ; 
the  oxide,  or  quick-lime,  CaO;  the  hydroxide,  or  slaked 
lime,  Ca(OH)2;  the  carbide,  CaC2;  the  hypochlorite. 
Ca(OCl)2;  the  carbonate,  CaC03;  the  sulphate,  CaS04;  the 
phosphate,  Ca3(P04)2;  and  the  silicate,  in  the  form  of  glass. 

322 


COMPOUNDS  OF  CALCIUM.  323 

Calcium  Chloride,  CaCl2. — The  property  which  gives 
this  salt  its  value  is  its  power  to  absorb  water.  It  is  used 
as  a  drying  agent.  Gases  are  passed  through  it  for  the 
purpose  of  drying  them,  and  it  is  also  placed  in  vessels  in 
which  it  is  necessary  that  the  atmosphere  should  be  dry. 

EXPERIMENT  152. — Dissolve  10  to  20  grams  of  limestone  or 
marble  in  ordinary  hydrochloric  acid.  Evaporate  the  solution  to 
dryness.  Expose  a  few  pieces  of  the  residue  to  the  air.  Does  it 
become  moist  ?  In  what  experiments  has  calcium  chloride  been 
used,  and  for  what  purposes  ?  What  would  happen  if  sulphuric 
acid  were  added  to  calcium  chloride?  Try  it.  Explain  what 
takes  place.  Is  the  residue  soluble  or  insoluble  in  water  ? 

Calcium  Oxide,  CaO. — This  is  the  substance  commonly 
called  lime,  or,  to  distinguish  it  from  the  hydroxide  or 
slaked  lime,  it  is  called  quick-lime.  It  is  made  by  heating 
calcium  carbonate,  which  is  thus  decomposed  into  lime 
and  carbon  dioxide : 

CaCO,  =  CaO  +  C02. 

Limekilns  are  large  furnaces  in  which  limestone  and 
other  forms  of  calcium  carbonate  are  heated  and  con- 
verted into  lime. 

[Why  is  it  dangerous  to  remain  for  any  length  of  time 
in  the  immediate  neighborhood  of  a  limekiln  ?] 

Lime  is  a  white,  amorphous,  infusible  substance.  When 
heated  in  the  flame  of  the  compound  blowpipe,  it  gives 
out  an  intense  light,  as  any  other  infusible  substance  would 
under  the  same  circumstances.  When  exposed  to  the  air, 
it  attracts  moisture  and  carbon  dioxide  and  is  thus  con- 
verted into  the  carbonate.  It  must  hence  be  protected 
from  the  air.  Lime  that  has  been  converted  into  the  car- 
bonate by  exposure  to  the  air  is  said  to  be  air-slaked. 

Calcium  Hydroxide,  Ca02H2,  or  Ca(OH)2.—  When  cal- 
cium oxide  or  quick-lime  is  treated  with  water,  it  becomes 


324  INTRODUCTION   TO  CHEMISTRY. 

hot  and  crumbles  to  a  fine  powder.  The  substance  formed 
in  this  operation  is  somewhat  soluble  in  water,  the  solution 
being  known  as  lime-water.  The  chemical  change  that 
takes  place  when  lime  is  treated  with  water  has  been  ex- 
plained. It  consists  in  the  formation  of  a  compound  of 
the  formula  Ca02H2  and  known  as  slaked  lime,  and  the 
operation  is  known  as  slaking.  It  is  believed  that  just  as 
potassium  hydroxide,  KOH,  is  properly  regarded  as  water 
in  the  molecule  of  which  one  atom  of  potassium  is  sub- 
stituted for  an  atom  of  hydrogen,  so  calcium  hydroxide  is 
properly  regarded  as  derived  from  water  by  the  substitu- 
tion of  an  atom  of  calcium  for  two  atoms  of  hydrogen  in 
two  molecules: 

HOH  C.)ggorCa(OH), 

Two  mol.  water.  Calcium  hydroxide. 

It  is  difficult  to  explain  exactly  why  this  view  is  held. 
It  can  only  be  said  that  it  is  a  conception  in  harmony  with 
a  great  many  facts,  though  it  does  not  follow  as  a  neces- 
sary consequence  from  any  facts  known  to  us. 

EXPERIMENT  153. — Moisten  40  to  50  grams  good  quick-lime 
with  water.  Soon  the  mass  will  begin  to  crumble,  and  steam 
will  rise  from  it,  indicating  that  heat  is  evolved.  Afterwards 
dilute  to  2  or  3  litres  and  put  the  whole  in  a  well-stoppered  bot- 
tle. The  undissolved  lime  will  settle  to  the  bottom,  and  in  the 
course  of  some  hours  the  solution  above  will  become  clear. 
Carefully  pour  off  some  of  the  clear  solution.  [What  takes  place 
when  some  of  the  solution  is  exposed  to  the  air?  when  the 
gases  from  the  lungs  are  passed  through  it  ?  when  carbon  dioxide 
is  passed  through  it?  What  takes  place  when  dilute  sulphuric 
acid  is  added  to  lime-water?  Is  calcium  sulphate  difficultly  or 
easily  soluble  in  water  ?  Has  lime-water  an  alkaline  reaction  ? 

When  potassium  hydroxide  is  added  to  a  solution  of  a 
salt  containing  a  metal  whose  hydroxide  is  insoluble  in 
water,  the  insoluble  hydroxide  is  precipitated.  This  was 


COMPOUNDS   OF  CALCIUM.  325 

illustrated  in  Experiments  132  and  133.  Calcium  hy- 
droxide is  a  soluble  hydroxide,  and  acts  in  the  same  way 
that  potassium  hydroxide  does. 

EXPERIMENT  154.— Add  some  lime-water  to  a  dilute  solution  of 
ferric  chloride,  of  copper  nitrate,  of  lead  nitrate.  Explain  the 
results. 

Uses. — Lime  is  extensively  used  in  the  arts,  generally  in 
the  form  of  the  hydroxide.  As  we  have  seen,  it  is  used 
in  the  preparation  of  ammonia  and  of  the  caustic  alkalies, 
potassium  and  sodium  hydroxides;  and  of  bleaching- 
powder  and  potassium  chlorate.  It  is  further  used  in 
large  quantity  in  the  process  of  tanning  for  removing  the 
hair  from  hides;  in  decomposing  fats  for  making  stearin 
for  candles;  for  purifying  illuminating-gas;  and  especially 
in  the  preparation  of  mortar. 

Calcium  Carbide,  CaC2. — This  compound  is  easily  formed 
by  heating  lime  and  coke  together  in  the  form  of  powder  in 
an  electric  furnace,  when  the  reaction  represented  below 
takes  place: 

CaO  +  30  =  CaC2  +  CO. 

It  is  a  crystallized  substance.  With  water  it  gives  acetylene 
and  lime.  (See  Acetylene. ) 

Calcium  Hypochlorite,  Ca(OCl)2,  has  already  been  re- 
ferred to  under  Chlorine.  The  form  in  which  chlorine  is 
transported  is  "  bleaching-powder,"  a  compound  con- 
taining calcium  hvpochlorite  and  calcium  chloride, 
Ca(OCl)2  -f-  CaCl2 ,  made  by  treating  slaked  lime  with 
chlorine : 

2Ca(OH)2  -f  4C1  =  Ca(OCl)2  +  CaCl2  +  2H20. 

V  J 

Bleacbing-powder. 


326  INTRODUCTION   TO  CHEMISTRY. 

The  compound  is  commonly  called  "  chloride  of  lime." 
An  objection  to  the  view  that  calcium  chloride  is  present 
as  such  in  bleaching-powder  is  found  in  fche  fact  that  the 
substance  is  not  deliquescent.  This  has  led  to  the  sug- 
gestion that  bleaching-powder  in  the  dry  form  is  not  a 
mixture  of  two  compounds  as  represented  above,  but  that 

Cl 
it  is  rather  one  compound  of  the  formula  Ca<™   or 


CaOCl2.  The  point  is  a  difficult  one  to  decide,  but  at 
present  the  evidence  appears  to  be  in  favor  of  the  view  that 
bleaching-powder  in  the  dry  form  is  a  single  compound  of 
the  constitution  represented  by  the  formula  last  given. 
When  treated  with  water,  however,  it  forms  the  ions  Ca, 
Cl,  and  OC1,  which  are  the  same  ions  that  would  be  formed 
by  dissolving  a  mixture  of  calcium  chloride  and  calcium 
hypochlorite. 

Properties,  —  Bleaching-powder  is  a  white  substance  that 
has  the  odor  of  hypochlorous  acid.  When  treated  with  an 
acid  it  gives  up  all  its  chlorine.  When  exposed  to  the 
action  of  carbon  dioxide  hypochlorous  acid  is  liberated. 
Hence  this  decomposition  takes  place  slowly  in  the  air. 

How  Bleaching-powder  Acts  in  Bleaching,  —  A  solution 
of  bleaching-powder  alone  is  not  capable  of  bleaching 
except  very  slowly.  If,  however,  something  is  added 
which  has  the  power  to  decompose  it,  bleaching  takes 
place,  the  action  being  due  to  the  presence  of  hypo- 
chlorous  acid  and  chlorine.  As  is  clear  from  what  was 
said  above,  the  passage  of  carbon  dioxide  through  the 
solution  or  the  addition  of  an  acid  would  cause  it  to 
bleach.  So,  too,  certain  salts  produce  a  similar  effect. 
The  explanation  of  this  is  the  instability  of  the  hypo- 
chlorites  formed  by  the  salts  added. 

Decomposition  of  Bleaching-powder  by  Boiling  its  Solu- 
tion, —  When  a  concentrated  solution  of  bleaching-powder 


CALCIUM  CARBONATE.  327 

is  heated  it  gives  off  oxygen,  and  the  salt  is  converted  into 
the  chloride.  In  dilute  solution,  however,  the  hypo- 
chlorite  is  converted  into  chlorate  and  chloride : 

3Ca(C10)2  =  Ca(C103)2  +  20aCl2. 

This  fact  is  taken  advantage  of,  as  has  been  shown,  for 
the  purpose  of  making  calcium  chlorate,  and  from  this 
potassium  chlorate  (see  p.  307).  In  contact  with  certain 
oxides,  as  copper  oxide,  ferric  oxide,  and  with  hydroxides, 
as  those  of  cobalt  and  nickel,  a  solution  of  bleaching- 
powder  readily  gives  up  oxygen  when  heated. 

Uses. — The  chief  application  of  bleaching-powder  is,  as 
its  name  implies,  for  bleaching.  It  is  also  used  as  a  dis- 
infectant and  as  an  antiseptic,  that  is,  for  the  purpose  of 
destroying  disease  germs  and  of  preventing  decomposition 
of  organic  substances. 

Calcium  Carbonate,  CaC03. — This  salt  occurs  in  im- 
mense quantities  in  nature  in  the  well-known  forms  lime- 
stone, calc-spar,  marble,  and  chalk.  The  variety  of 
calc-spar  found  in  Iceland,  and  known  as  Iceland  spar,  is 
particularly  pure  calcium  carbonate.  It  crystallizes  in  a 
number  of  different  forms,  the  most  common  being  rhom- 
bohedrons,  as  seen  in  ordinary  calc-spar.  A  second  variety 
of  crystallized  calcium  carbonate  is  aragonite.  This  is 
found  in  nature  crystallized  in  rhombic  prisms,  and  in 
forms  derived  from  this.  When  heated,  aragonite  falls 
to  pieces,  the  particles  being  small  crystals  of  the  form 
characteristic  of  calc-spar.  This  is  a  case  of  dimorphism 
similar  to  that  presented  by  sulphur,  which,  it  will  be 
remembered,  crystallizes  in  two  forms,  rhombic  and  mono- 
clinic,  the  latter  of  which  passes  into  the  former  spon- 
taneously. These  forms  are  produced  artificially  very 
readily.  When  calcium  carbonate  is  precipitated  from  a 


328  INTRODUCTION   TO  CHEMISTRY. 

solution  of  a  calcium  salt  by  adding  a  soluble  carbonate  at 
ordinary  temperatures,  the  precipitate  is  made  up  of 
microscopic  crystals  which  have  the  same  form  as  calc-spar. 
If,  however,  the  solution  from  which  the  carbonate  is  pre- 
cipitated is  hot,  the  salt  consists  of  microscopic  crystals  of 
the  form  of  aragonite. 

The  most  abundant  form  of  calcium  carbonate  is  lime- 
stone, of  which  many  great  mountain-ranges  are  largely 
made  up.  This  is  a  compact  form  of  the  compound, 
which  has  a  gray  color,  and  frequently  consists  of  minute 
crystals.  It  is  always  more  or  less  impure,  containing  clay 
and  other  substances.  Limestone  which  is  mixed  with  a 
considerable  proportion  of  clay  is  called  marl.  Many 
natural  waters  contain  calcium  carbonate  in  solution — 
probably  in  the  form  of  the  acid  carbonate.  When  such 
a  water  evaporates,  the  carbonate  is  deposited.  It  happens 
in  some  places  that  a  water  charged  with  the  carbonate 
works  its  way  slowly  through  the  earth  and  drops  from  the 
top  of  a  cave.  Under  these  circumstances  there  is  a 
gradual  deposit  of  the  salt  which  remains  suspended. 
Such  hanging  formations  of  the  carbonate  are  known  as 
stalactites.  At  the  same  time  that  part  of  the  liquid  which 
falls  to  the  bottom  of  the  cave  forms  a  projecting  mass 
below  the  stalactite.  Such  projecting  masses  are  called 
stalagmites.  The  formation  of  stalactites  takes  place  in 
somewhat  the  same  way  as  that  of  icicles. 

Much  of  the  calcium  carbonate  found  in  nature  has  its 
origin  in  the  remains  of  animals,  and  fossils  are  very 
abundant  in  it.  Chalk  consists  almost  exclusively  of  the 
shells  of  microscopic  animals. 

Temporary  Hardness, — When  carbon  dioxide  is  passed 
into  a  solution  of  calcium  hydroxide,  the  carbonate  is  pre- 
cipitated; and,  if  the  current  of  gas  is  continued  long 
enough,  the  carbonate  is  redissolved.  On  heating  the 


CALCIUM  SULPHATE.  329 

solution  to  boiling,  the  normal  carbonate  is  precipitated 
and  carbon  dioxide  is  given  off.  Natural  waters  that  come 
in  contact  with  limestone  gradually  take  up  more  or  less 
of  the  carbonate,  because  of  the  carbon  dioxide  dissolved 
in  them,  and  when  such  a  water  is  boiled,  the  carbonate 
is  thrown  down.  A  water  containing  calcium  carbonate 
in  solution  is  called  a  hard  water;  and,  as  this  kind  of 
hardness  is  easily  removed  by  boiling,  it  is  called  tempo- 
rary hardness  in  order  to  distinguish  it  from  a  kind  which 
is  not  removed  by  boiling,  and  therefore  called  permanent 
hardness.  Further,  temporary  hardness  is  removed  by 
adding  lime  to  the  water,  when  the  normal  carbonate  is 
formed,  which  is  at  once  precipitated. 

The  decomposition  of  calcium  carbonate  by  heat,  form- 
ing lime,  or  calcium  oxide,  and  carbon  dioxide,  was 
referred  to  on  p.  323. 

Applications. — Calcium  carbonate  is  used,  in  the  arts, 
for  a  great  many  purposes,  as  in  the  manufacture  of  glass; 
as  a  flux  in  many  important  metallurgical  operations,  as 
in  the  reduction  of  iron  from  its  ores;  in  the  preparation 
of  lime  for  mortar,  etc.  As  is  well  known,  further, 
marble  and  some  of  the  varieties  of  limestone  are  exten- 
sively used  in  building;  and  large  quantities  of  chalk  are 
also  used. 

Calcium  Sulphate,  CaS04.  —  This  compound  is  very 
abundant  in  nature.  The  principal  natural  variety  is 
gypsum,  which  occurs  in  crystals  containing  two  molecules 
of  water,  CaSO,  +  2H30.  The  salt  of  the  formula  CaS04 
also  occurs  in  nature,  and  is  called  anhydrite.  A  granular 
form  of  gypsum  is  called  alabaster.  Calcium  sulphate  is 
difficultly  soluble  in  hot  and  cold  water.  When  heated  to 
100°,  or  a  little  above,  it  loses  nearly  all  of  its  water  and 
forms  a  powder  known  as  plaster  of  Paris,  which  has  the 
power  of  taking  up  water  and  forming  a  solid  substance. 


33°  INTRODUCTION   TO  CHEMISTRY. 

This  process  of  solidification  is  known  as  "setting/' 
Plaster  of  Paris  is  very  largely  used  in  making  casts,  on 
account  of  its  power  to  harden  after  having  been  made 
into  a  paste  with  water.  The  hardening  is  a  chemical 
process,  and  is  caused  by  the  combination  of  water  with 
the  salt  to  form  the  crystallized  variety. 

When  heated  to  200°,  and  above,  all  the  water  is  given 
off  from  gypsum,  and  the  product  now  combines  with 
water  only  very  slowly,  and  is  of  no  value  for  making  casts. 
In  general,  the  higher  the  temperature  to  which  the 
gypsum  is  heated,  the  greater  the  difficulty  with  which  the 
product  combines  with  water. 

EXPERIMENT  155.— Heat  some  gypsum  to  between  140°  and  160° 
in  an  air-bath.  Examine  the  residue  and  see  whether  it  will 
become  solid  when  mixed  with  a  little  water  so  as  to  form  a  paste. 

Permanent  Hardness. — Many  natural  waters  contain 
gypsum  in  solution.  Such  waters  act  in  some  respects  like 
those  which  contain  calcium  carbonate.  With  soap,  for 
example,  they  form  insoluble  compounds.  This  kind  of 
hardness  is  not  removed  by  boiling,  and  it  is  therefore 
called  permanent  hardness.  Magnesium  sulphate  acts  in 
the  same  way,  producing  permanent  hardness. 

Action  of  Soluble  Carbonates  on  Gypsum. — When  cai- 
cium  sulphate  is  treated  with  a  solution  of  a  soluble  car- 
bonate, it  is  decomposed,  forming  calcium  carbonate  as 
represented  in  the  equation 

CaS04  -f  Na2C03  =  Na2S04  -f  CaC03. 

This  change  is  effected  simply  by  allowing  the  two  to 
stand  in  contact  at  the  ordinary  temperature. 

EXPERIMENT  156. — Upon  a  gram  or  two  of  powdered  gypsum 
pour,  say,  50  cc.  of  a  moderately  strong  solution  of  ammonium 
carbonate.  After  a  few  hours  pour  off  the  solution,  collect  the 
powder  on  a  filter,  wash  it  thoroughly  with  water  and  see 


CALCIUM  PHOSPHATE.  331 

whether  it  has  changed  to  the  carbonate.  [How  can  you  deter- 
mine whether  ammonium  sulphate  is  in  solution  or  not?  Of 
course,  there  is  still  ammonium  carbonate  present,  and  this  must 
be  taken  into  account  in  examining  for  the  sulphate.  We  usually 
examine  for  a  sulphate  by  adding  a  soluble  barium  salt,  when,  if 
a  soluble  sulphate  is  present,  barium  sulphate  is  precipitated.  In 
this  case,  however,  the  ammonium  carbonate  would  throw  down 
barium  carbonate.  To  prevent  this,  the  ammonium  carbonate  is 
decomposed  by  slowly  adding  sufficient  dilute  hydrochloric  acid. 
There  will  then  be  present  ammonium  chloride  and  sulphate  ; 
and,  now,  if  barium  chloride  or  any  other  soluble  barium  salt  is 
added,  barium  sulphate  is  precipitated.] 

Uses. — Besides  its  use  for  making  casts,  calcined  gypsum 
is  used  also  in  surgery  for  making  plaster-of-Paris 
bandages,  and  as  a  fertilizer.  Its  action  as  a  fertilizer  is 
thought  by  some  to  be  due  to  the  fact  that  it  has  the  power 
to  hold  ammonia  and  ammonium  carbonate  in  combina- 
tion, and  thus  to  make  them  available  for  the  plants.  It 
has  been  shown  that  it  in  some  way  facilitates  the  process 
of  nitrification,  and  perhaps  it  is  in  consequence  of  this 
that  it  aids  plant-growth. 

Calcium  Phosphates. — There  are  three  phosphates  of 
calcium:  (1)  the  normal  phosphate,  Ca3(POJ2;  (2)  the 
secondary  phosphate,  CaHP04;  and  (3)  the  primary  phos- 
phate, CaH4(PO,)2. 

Normal  calcium  phosphate  is  found  in  nature  in  large 
quantity  as  phosphorite,  and  in  combination  with  calcium 
fluoride  or  chloride  as  apatite.  It  is,  further,  the  principal 
inorganic  constituent  of  bones,  forming  85  per  cent  of 
bone-ash. 

Calcium  Phosphate  Essential  to  Plant-growth. — Calcium 
phosphate  is  found  everywhere  in  the  soil,  and  is  taken  up 
by  the  plants  for  whose  growth  it  is  essential.  That  it  is 
also  essential  to  the  life  of  animals  is  obvious  from  the  fact 


332  INTRODUCTION   TO   CHEMISTRY. 

that  the  bones  consist  so  largely  of  it.  The  phosphate 
required  for  the  building  up  of  bones  is  taken  into  the 
system  with  the  food.  From  these  statements  it  is  clear 
that  calcium  phosphate  is  of  fundamental  importance,  and 
that  a  fertile  soil  must  either  contain  this  salt,  or  some- 
thing from  which  it  can  be  formed.  Now,  when  a  crop 
is  raised  on  a  given  area,  a  certain  amount  of  the  phos- 
phate contained  in  it  is  withdrawn.  If  the  plants  were 
allowed  to  decay  where  they  grow,  the  phosphate  would 
be  returned  and  the  soil  would  continue  fertile;  but  in 
cultivated  land  this  is  not  the  case.  The  crops  are 
removed,  and  with  them  the  calcium  phosphate,  and  the 
soil  therefore  becomes  exhausted.  If  the  substances 
removed  are  used  as  food,  some  of  the  phosphate  is  found 
in  the  excrement  of  the  animals;  and,  if  the  excrement  is 
put  on  the  soil,  this  is  again  rendered  fertile. 

Artificial  Fertilizers. — There  are,  however,  other  sources 
of  calcium  phosphate,  and  some  of  these  are  utilized  ex- 
tensively in  the  preparation  of  artificial  fertilizers.  The 
natural  form  of  the  phosphate,  as  that  in  bone-ash,  in 
phosphorite,  and  in  guano,  is  mainly  the  normal  or 
neutral  phosphate.  This  is  insoluble  in  water,  and  is 
therefore  taken  up  by  the  plants  with  difficulty.  To  make 
it  quickly  available,  it  must  be  converted  into  a  soluble 
phosphate.  This  is  done  by  treating  it  with  sulphuric  acid 
in  order  to  effect  the  reaction  represented  in  this  equation  : 

Ca3(p°J2  +  2H2S04  =  CaH4(P04)2  +  2CaS04. 

The  primary  phosphate  thus  formed  is  soluble  in  water, 
and  is  of  great  value  as  a  fertilizer.  The  mixture  of  the 
soluble  phosphate  and  of  calcium  sulphate  is  known  as 
"superphosphate  of  lime."  The  sulphate,  as  we  have 
seen,  is  also  of  value  as  a  fertilizer.  The  value  of  super- 
phosphates depends  mostly  upon  the  amount  of  soluble 


CALCIUM  PHOSPHATE.  333 

phosphate  contained  in  them :  and  in  dealing  with  them  it 
is  customary  to  state  how  much  "  soluble"  and  how  much 
' '  insoluble  phosphoric  acid "  they  contain.  When  a 
superphosphate  is  allowed  to  stand  for  a  time,  some  of  the 
soluble  primary  phosphate  is  converted  into  insoluble 
phosphates  by  contact  with  basic  hydroxides  and  water. 
This  is  known  as  the  process  of  "  reversion,"  and  that  part 
of  the  phosphoric  acid  which  is  contained  in  the  insoluble 
phosphate  is  spoken  of  as  "reverted  phosphoric  acid." 

Formation   of  Calcium   Phosphate   by  Precipitation. — 

Normal  calcium  phosphate,  as  has  been  stated,  is  insoluble 
in  water,  and  is  formed  when  a  soluble  normal  phosphate 
is  added  to  a  solution  of  a  calcium  salt.  It  is  also  formed 
when  disodium  phosphate  and  ammonia  are  added  to  a 
solution  of  a  calcium  salt,  thus: 
2HNa2PO4  +  3CaCla  +  2NH3  =  Ca.(PO4)a  +  4Na01  +  2NH401. 

EXPERIMENT  157. — To  a  solution  of  calcium  chloride  in  a  test- 
tube  add  disodium  phosphate  and  ammonia.  Tho  precipitate  will 
dissolve  in  hydrochloric  or  nitric  acid. 

Primary  calcium  phosphate,  CaH4(P04)2,  is  commonly 
called  the  acid  phosphate  of  calcium.  It  is  formed  when 
ordinary  insoluble  calcium  phosphate  is  treated  with  con- 
centrated sulphuric  acid,  and  is  contained  in  the  so-called 
superphosphates. 

Calcium  silicate,  CaSi03,  occurs  in  nature  as  the  min- 
eral wollastonite,  and,  in  combination  with  other  silicates, 
in  a  large  number  of  minerals,  as  garnet,  mica,  etc.  It  is 
formed  when  a  solution  of  sodium  silicate  is  added  to  a 
solution  of  calcium  chloride,  and  when  a  mixture  of  cal- 
cium carbonate  and  quartz  is  heated  to  fusion. 

Glass. — Ordinary  glass  is  a  silicate  of  calcium  and  sodium 
made  by  melting  sand  (silicon  dioxide,  silica,  SiOJ  with 


334  INTRODUCTION   TO  CHEMISTRY. 

lime  and  sodium  carbonate  (soda)  or  sodium  sulphate. 
Instead  of  calcium  carbonate,  lead  oxide  may  be  used ;  and 
instead  of  sodium  carbonate,  potassium  carbonate.  The 
properties  of  the  glass  are  dependent  upon  the  materials 
used  in  its  manufacture. 

Ordinary  window-glass  is  a  sodium-calcium  glass.  The 
purer  the  calcium  carbonate  and  silica,  the  better  the 
quality  of  the  glass.  This  glass  is  comparatively  easily 
acted  upon  by  chemical  substances,  and  is  therefore  not 
adapted  to  the  preparation  of  vessels  that  are  to  be  used  to 
hold  acids  and  other  chemically  active  substances.  It 
answers,  however,  very  well  for  windows.  The  difference 
between  ordinary  window-glass  and  plate  glass  is  essentially 
that  the  former  is  blown  and  then  cut  into  pieces,  while 
the  latter,  when  in  the  molten  condition,  is  run  into  flat 
moulds  and  there  allowed  to  solidify. 

Bohemian  glass  is  made  with  potassium  carbonate.  If 
pure  carbonate  is  used,  as  well  as  pure  calcium  carbonate 
and  silica,  a  very  beautiful  glass  is  the  result.  It  is  char- 
acterized by  great  hardness,  by  its  difficult  fusibility,  and 
by  its  resistance  to  the  action  of  chemical  substances.  It 
is  particularly  well  adapted  to  the  manufacture  of  vessels 
for  use  in  chemical  laboratories. 

Flint-glass  is  made  by  melting  together  lead  oxide, 
potassium  carbonate,  and  silicon  dioxide.  It  is  charac- 
terized by  its  power  to  refract  light,  its  high  specific 
gravity,  its  low  melting-point,  and  the  ease  with  which  it 
is  acted  upon  by  reagents.  Owing  to  its  high  refractive 
power,  it  is  largely  used  in  the  manufacture  of  lenses  for 
optical  instruments. 

Strass  is  a  variety  of  lead-glass  that  is  particularly  rich 
in  lead.  Its  refracting  power  is  so  great  that  it  is  used  in 
the  manufacture  of  artificial  gems. 

Colors  are  given  to  glass  by  putting  into  the  fused  mass 
small  quantities  of  various  substances.  Thus,  a  cobalt 


GLASS    MORTAR  335 

compound  makes  glass  blue;  copper  aud  chromium  make 
it  green ;  one  of  the  oxides  of  copper  makes  it  red ;  uranium 
gives  it  a  yellow  color,  etc.  The  most  common  variety  of 
glass  is  that  used  in  the  manufacture  of  ordinary  bottles. 
It  is  generally  green  to  black,  and  sometimes  brown.  In 
its  manufacture  impure  materials  are  used,  chiefly  ordi- 
nary sand,  limestone,  sodium  sulphate,  common  salt,  clay, 
etc. 

Glass  which  has  been  suddenly  cooled  is  very  brittle  and 
breaks  into  small  pieces  when  scratched  or  slightly  broken 
in  any  way.  This  is  shown  by  the  so-called  Prince 
Rupert's  drops,  which  are  made  by  dropping  glass,  in  the 
molten  condition,  into  water.  When  the  end  of  such  a 
drop  is  broken  off,  the  entire  mass  is  completely  shattered 
into  minute  pieces.  It  is  clear  from  this  that,  in  the 
manufacture  of  glass  objects,  care  must  be  taken  not  to 
cool  them  suddenly.  In  fact  they  are  cooled  very  slowly, 
the  process  being  known  as  annealing.  For  this  purpose 
they  are  placed  in  furnaces  the  temperature  of  which  is 
but  little  below  that  of  fusion,  and  are  kept  there  for  some 
time,  the  heat  being  gradually  lowered.  If  red-hot  glass 
is  introduced  into  heated  oil  or  paraffin,  and  allowed  to 
cool,  it  is  found  to  be  extremely  hard  and  elastic.  The 
glass  of  De  la  Bastie  is  made  in  this  way.  Vessels  made 
of  it  can  be  thrown  about  upon  hard  objects  without  break- 
ing, but  sometimes  a  slight  scratch  will  cause  the  glass  to 
fly  to  pieces,  as  the  Rupert's  drops  do. 

Mortar. — Mortar  is  made  of  slaked  lime  and  sand. 
When  this  mixture  is  exposed  to  the  air,  carbonate  of 
calcium  is  slowly  formed,  and  the  mass  becomes  extremely 
hard.  The  water  contained  in  the  mortar  soon  passes  off, 
but  nevertheless  freshly-plastered  rooms  remain  moist  for 
a  considerable  time.  This  is  due  to  the  fact  that  a  reaction 
is  constantly  taking  place  between  the  carbon  dioxide  and 


336  INTRODUCTION   TO  CHEMISTRY. 

calcium  hydroxide  by  which  calcium  carbonate  and  water 
are  formed, 

Ca(OH)2  +  002  =  CaC03  +  H20, 

and  it  is  the  water  thus  liberated  that  keeps  the  air  moist. 
The  complete  conversion  of  the  lime  into  carbonate  re- 
quires a  very  long  time,  because  the  carbonate  which  is 
formed  on  the  surface  protects  the  lime  in  the  interior 
to  some  extent. 

It  is  generally  regarded  as  unhealthy  to  live  in  rooms 
with  freshly-plastered  walls,  because  the  air  is  constantly 
kept  moist  in  consequence  of  the  reaction  above  mentioned. 
It  is,  however,  difficult  to  see  why  the  presence  of  a  little 
extra  moisture  in  the  air  should  be  unhealthy;  and,  if 
there  is  any  danger  from  freshly-plastered  walls,  it  seems 
probable  that  the  cause  must  be  sought  elsewhere.  It  is 
possible  that  the  constant  presence  of  moisture  in  the 
pores  of  the  walls  interferes  with  the  important  process  of 
diffusion,  and  that  therefore  when  the  room  is  closed  this 
natural  method  of  ventilation  cannot  come  into  play. 

Cements. — When  lime-stones  that  contain  magnesium 
carbonate  and  aluminium  silicate  in  considerable  quantities 
are  heated  for  the  preparation  of  lime,  the  product  does 
not  act  with  water  as  calcium  oxide  does,  and  this  lime  is 
not  adapted  to  the  preparation  of  ordinary  mortar.  On 
the  other  hand,  it  gradually  becomes  solid,  in  contact  with 
water,  for  reasons  which  are  not  known.  Such  substances 
are  known  as  cements,  or  hydraulic  cements.  Other  cements 
besides  those  made  in  the  manner  mentioned  are  known. 

Calcium  sulphide,  CaS,  is  formed  by  heating  calcium 
sulphate  with  charcoal.  It  is  remarkable  on  account  of 
the  fact  that  it  is  phosphorescent.  After  having  been 
exposed  to  sunlight,  it  continues  to  give  light  for  some 


BARIUM  AND  STRONTIUM.  337 

time  afterward.  This  and  the  similar  compound,  barium 
sulphide,  are  used  to  some  extent  in  the  preparation  of 
luminous  objects,  such  as  match-boxes,  clock-faces,  plates 
for  house-numbers,  etc. 

Barium  and  Strontium. — The  compounds  of  barium  and 
strontium  closely  resemble  those  of  calcium.  Barium 
forms  an  oxide,  BaO,  corresponding  to  lime,  and  also 
another  one  known  as  barium  dioxide,  Ba02.*  This  is 
formed  by  passing  oxygen  or  air  over  barium  oxide  heated 
to  a  dull  red  heat.  At  a  higher  temperature  it  gives  off 
the  oxygen.  These  facts  have  been  utilized  for  the  pur- 
pose of  extracting  oxygen  from  the  air. 

•  Barium  oxide  is  converted  into  the  hydroxide,  Ba(OH)2 , 
when  treated  with  water.     This  hydroxide  is   soluble  in 
water,  the  solution  being  known  as  baryta-water. 

Flame  Reactions. — Calcium  compounds  color  the  flame 
reddish  yellow;  strontium  compounds,  intense  red;  and 
barium  compounds,  yellowish  green. 

Relations  between  the  Atomic  Weights  of  the  Members 
of  this  Group. — Between  the  atomic  weights  of  calcium, 

*  This  compound  lias  already  been  referred  to  in  describing  the 
preparation  of  hydrogen  dioxide,  H3Oa.     When  it  is  treated   with 
sulphuric  acid  this  reaction  takes  place  : 

BaO,  +  HaS04  =  BaS04  -f-  HaOa. 

When  barium  oxide,  BaO,  is  treated  with  sulphuric  acid  this  reac- 
tion takes  place  : 

BaO  -f  HaSO4  =  BaSO4  -f  HaO. 

When  barium  dioxide  is  treated  with  hydrochloric  acid,  hydrogen 
dioxide  is  also  formed  thus  : 

Ba02  +  2HC1  =  Bad,  -f  Ha02. 

[Compare  this  with  the  action  that  takes  place  when  hydrochloric 
acid  acts  upon  manganese  dioxide. 


338  INTRODUCTION   TO  CHEMISTRY. 

strontium,  and  barium  there  exists  the  same  relation  as 
that  with  which  we  are  already  familiar  in  other  groups. 
The  atomic  weight  of  calcium  is  40;  of  strontium,  87.6; 
and  of  barium,  137.4: 

40  +137'4  =  88.7. 


CHAPTER   XXII. 

THE  MAGNESIUM   GROUP: 
MAGNESIUM,   ZINC,   CADMIUM. 

OF  the  three  members  of  this  group,  magnesium  and 
zinc  are  by  far  the  most  common. 

Magnesium  Mg  (At.  Wt.  24.36). — Magnesium  occurs 
very  widely  distributed  in  nature,  and  in  considerable 
quantities.  Among  the  important  magnesium  minerals 
are  carnallite,  MgCl2.KCl  -f  6H20,  or  MgK013  +  6H20; 
magnesite,  which  is  the  carbonate  MgC03;  dolomite,  a 
double  carbonate  of  magnesium  and  calcium;  soapstone, 
serpentine,  and  meerschaum,  which  is  essentially  a  silicate 
of  magnesium.  Further,  there  are  many  silicates  that 
contain  magnesium,  among  them  being  asbestos  and  horn- 
blende. The  metal  is  also  found  in  solution  in  many 
spring- waters  in  the  form  of  the  sulphate,  or  Epsom  salt. 

Manufacture. — It  is  prepared  by  electrolysis  of  de- 
hydrated carnallite,  MgKCl3.  This  is  melted  in  an  iron 
crucible.  One  pole  of  the  battery  is*  a  piece  of  carbon,  the 
other  is  the  crucible  itself. 

Properties. — It  is  a  silver-white  metal  with  a  high  lustre. 
In  the  air  it  changes  only  slowly,  but  gradually  becomes 
covered  with  a  layer  of  the  oxide.  When  heated  above  its 
melting-point  in  the  air  it  burns  with  a  bright  flame, 

339 


340  INTRODUCTION    TO   CHEMISTRY. 

forming  the  white  oxide  and  some  nitride,  MgsN2.  The 
light  of  the  flame  is  very  efficient  in  producing  certain 
chemical  changes,  such  as  the  combination  of  hydrogen 
and  chlorine.  At  ordinary  temperatures  magnesium  does 
not  decompose  water;  at  100°  it  decomposes  it  slowly. 
[Note  the  marked  difference  in  this  respect  between  mag- 
nesium and  the  alkali  metals.] 

Applications, — The  principal  use  to  which  magnesium 
is  put  is  for  producing  a  bright  light,  as  for  photographing 
in  spaces  to  which  the  sunlight  does  not  have  access,  and 
for  signalling.  The  so-called  "  flash-light "  is  produced 
by  burning  magnesium  powder.  It  is  also  used  to  some 
extent  as  an  ingredient  of  materials  employed  in  making 
fireworks. 

Compounds  of  Magnesium. — The  chief  compounds  of 
magnesium  are  the  oxide,  MgO,  called  magnesia  ;  the  sul- 
phate, MgS04  -f-  7H20,  commonly  called  Epsom  salt;  the 
carbonate,  MgC03;  the  silicates;  and  the  chloride,  MgCl2. 

Magnesium  Oxide,  MgO. — This  compound  is  commonly 
called  magnesia.  A  fine  white  variety  made  by  heating 
precipitated  magnesium  carbonate  is  called  magnesia  usta. 
It  is  very  difficultly  soluble  in  water,  forming  with  it  mag- 
nesium hydroxide,  Mg(OH)2,  which  is  very  difficultly 
soluble  in  water.  [What  difference  is  there  between  mag- 
nesium and  calcium  in  this  respect  ?] 

Magnesium  chloride,  MgCl2 ,  is  of  special  interest  for  the 
reason  that  it  is  the  compound  from  which  the  metal 
magnesium  was  first  made.  It  is  prepared  by  dissolving 
the  carbonate  in  hydrochloric  acid.  On  evaporating  this 
solution  to  the  proper  concentration,  crystals  of  magnesium 
chloride  containing  water  of  crystallization,  MgCl2  -j-  6H,0, 


MAGNESIUM  SULPHATE.  341 

are  deposited.  When  this  compound  is  heated  for  the 
purpose  of  drying  it,  the  larger  part  of  it  undergoes  decom- 
position, thus: 

MgCl2  -f  H20  =  MgO  +  2HC1. 

Tho  same  thing  takes  place  to  some  extent  on  heating 
calcium  chloride  with  water,  so  that  fused  calcium  chloride 
is  always  slightly  alkaline  in  consequence  of  the  presence 
of  lime,  or  calcium  oxide. 

Dry  magnesium  chloride  is  prepared  by  adding  am- 
monium chloride  to  its  solution  and  evaporating  to  dryness. 
A  double  chloride  of  the  composition,  Mg012.  NH4C1,  is 
formed  which  can  be  evaporated  to  complete  dryness  with- 
out decomposition.  When  perfectly  dry  this  double  salt 
breaks  down  at  a  high  temperature  into  ammonium 
chloride  and  magnesium  chloride.  The  ammonium  chlo- 
ride is  volatilized,  and  the  magnesium  chloride  remains 
behind. 

Magnesium  Sulphate,  MgS04. — The  mineral  kieserite, 
which  occurs  at  Stassfurt,  has  the  composition  MgS04  -f- 
H20.  The  salt  MgS04  -f  7H20  also  occurs  in  nature.  It 
is  this  variety  which  is  generally  obtained  when  a  solution 
of  magnesium  sulphate  is  evaporated  to  crystallization. 
Its  water  solution  has  a  bitter,  salty  taste. 

EXPERIMENT  158. — Make  some  magnesium  sulphate  by  dissolv- 
ing magnesite  (say  20  grams)  in  dilute  sulphuric  acid,  filtering 
and  evaporating  to  crystallization.  Pour  off  the  mother-liquor, 
and  dry  the  crystals  by  laying  them  on  several  sheets  of  filter- 
paper. 

Uses. — Magnesium  sulphate  finds  extensive  application. 
It  is  used  in  medicine  as  a  purgative,  and  is  known  as 
Epsom  salt,  as  it  is  contained  in  the  water  of  Epsom 
springs.  It  is  used,  further,  in  the  manufacture  of  sodium 
sulphate  and  potassium  sulphate,  and  as  a  fertilizer  in 


342  INTRODUCTION   TO  CHEMISTRY. 

place  of  gypsum.     Its  chief  use  is  as  a  dressing  for  cotton 
goods. 

Zinc,  Zn  (At.  Wt,  65.4). — Zinc,  in  almost  all  its  com- 
pounds, exhibits  a  close  resemblance  to  magnesium.  It 
occurs  in  nature  in  combination  principally  as  the  car- 
bonate, or  smithsonite,  ZnC03;  as  the  sulphide,  or  sphale- 
rite, ZnS;  and  as  the  silicate,  Zn2Si04.  Among  other 
compounds  of  zinc  found  in  nature  are  gahnite,  Zn(A102)., , 
and  franklinite,  which  contains  the  compound  Zn(Fe02).2 
together  with  the  analogous  compound  of  iron,  Fe(Fe02).,. 

Metallurgy. — The  metallurgy  of  zinc  is  much  simpler 
than  that  of  magnesium,  for  the  reason  that  the  ores  are 
easily  converted  into  the  oxide  by  roasting,  and  the  oxide 
is  easily  reduced  by  heating  it  with  charcoal.  Owing  to 
the  volatility  of  the  metal  the  vessels  in  which  the  reduc- 
tion is  effected  must  be  so  constructed  as  to  facilitate  the 
condensation  of  the  vapor.  The  vessels  used  are  either 
earthenware  muffles  or  tubes,  open  at  one  end  and  con- 
nected with  iron  receivers.  At  first  the  zinc  vapor  is 
condensed  in  the  form  of  a  fine  dust,  as  in  the  case  of 
sulphur.  This  forms  the  commercial  product  called  zinc 
dust.  It  always  contains  zinc  oxide.  Afterwards  the  zinc 
condenses  to  the  form  of  a  liquid,  and  this  is  cast  in  plates. 
The  zinc  thus  obtained  is  not  pure,  but  contains  lead  and 
iron,  and  sometimes  arsenic  and  cadmium.  It  is  called 
spelter.  By  repeated  distillation  it  can  be  obtained  pure. 
When  distilled  under  diminished  pressure,  it  is  deposited 
in  beautiful  lustrous  crystals,  the  forms  of  which  are 
extremely  complicated. 

Pure  zinc  is  obtained  by  the  electrolysis  of  solutions  of 
zinc  chloride. 

Properties. — Zinc  has  a  bluish-white  color  and  a  high 
lustre.  The  crystals  above  referred  to,  which  are  perfectly 


ZINC.  343 

pure  zinc,  have  a  brilliant  lustre  and  do  not  change  in  the 
air.  At  different  temperatures  zinc  has  markedly  different 
properties.  At  ordinary  temperatures  it  is  quite  brittle; 
at  100°-150°  it  can  be  rolled  out  in  sheets,  but  above  200° 
it  becomes  brittle  again.  It  melts  at  433°,  and  boils  at 
1040°.  When  heated  in  the  air  it  takes  fire,  and  burns 
with  a  bluish  flame,  forming  zinc  oxide.  This  can  be 
shown  by  means  of  the  oxyhydrogen  blowpipe.  In  dry  air 
it  does  not  change.  Ordinary  zinc  dissolves  in  all  the 
common  acids,  usually  with  evolution  of  hydrogen.  In 
the  case  of  nitric  acid,  however,  the  acid  is  to  some  extent 
reduced  to  ammonia.  The  purer  the  zinc  the  less  readily 
is  it  acted  upon  by  sulphuric  acid,  and  the  pure  crystals 
above  referred  to  are  scarcely  acted  upon  at  all  by  this 
acid.  Zinc  also  dissolves  in  the  caustic  alkalies,  forming 
zincates.  Pure  zinc  can  be  made  to  act  upon  sulphuric 
acid  by  adding  a  few  drops  of  platinum  chloride. 

Applications. — Zinc  is  extensively  used  as  sheet-zinc,  in 
making  galvanic  batteries,  for  galvanizing  iron,  etc.  Zinc 
dust  is  a  very  efficient  reducing  agent,  either  in  alkaline 
or  in  acid  solution.  With  caustic  alkalies — as,  for  exam- 
ple, with  potassium  hydroxide — it  gives  hydrogen  and  a 
zincate : 

Zn  +  2KOH  =  Zn(OK)2  -f  H2. 

With  sulphuric  acid  also  it  gives  hydrogen  readily.  Zinc 
is  used  in  the  preparation  of  important  alloys. 

Alloys. — Iron  covered  with  a  layer  of  zinc  is  known  as 
galvanized  iron.  Zinc  is  also  a  constituent  of  brass.  It 
combines  readily  with  mercury  to  form  zinc  amalgam,  and 
this  fact  is  taken  advantage  of  for  the  purpose  of  preserv- 
ing the  zinc  plates  in  galvanic  batteries.  Zinc  plates 
covered  with  a  layer  of  the  amalgam  are  acted  upon  much 
more  slowly  than  zinc  itself.  The  amalgamation  is  effected 


344  INTRODUCTION   TO  CHEMISTRY. 

by  cleaning  the  zinc,  dipping  it  in  dilute  sulphuric  acid, 
and  rubbing  mercury  over  the  surface  with  a  brush  or  a 
piece  of  cloth. 

Zinc  oxide,  ZnO,  is  obtained  as  Flores  zinci  by  burning 
zinc,  and  by  heating  the  carbonate  or  nitrate  of  zinc.  It 
turns  yellow  when  heated,  but  on  copling  becomes  white 
again. 

EXPERIMENT  159.— Heat  a  small  piece  of  zinc  on  charcoal  in 
the  oxidizing  flame  of  the  blowpipe.  The  white  fumes  of  zinc 
oxide  (philosopher's  wool)  will  be  seen,  and  the  charcoal  will  be 
covered  with  a  film  which  is  yellow  while  hot,  but  becomes  white 
on  cooling.  [What  element  gives  a  film  which  is  white  both  when 
hot  and  when  cold?] 

Zinc  oxide  is  used  as  a  constituent  of  paint  under  the 
name  of  zinc  white. 

Zinc  sulphate,  ZnS04  +  ?H20,  is  commonly  called  white 
vitriol.  [In  what  experiments  has  zinc  sulphate  been 
obtained  ?]  It  is  obtained  on  the  large  scale  by  heating 
zinc  sulphide  in  contact  with  the  air.  Under  these  cir- 
cumstances, the  sulphide  is  oxidized : 

ZnS  +  40  —  ZnS04. 

This  operation  is  known  as  roasting.  By  roasting  zinc 
sulphide  at  a  higher  temperature  it  is  converted  into  zinc 
oxide : 

ZnS  +  30  =  ZnO  +  S02. 

Zinc  sulphate  is  also  formed  in  large  quantities  in  gal- 
vanic batteries  and  in  the  preparation  of  hydrogen. 

Zinc  chloride,  ZnCl2,  is  obtained  by  evaporating  a  water 
solution  of  the  substance  and  distilling  the  residue.  It  is 
an  oily  liquid  which  has  a  very  strong  affinity  for  water. 


SOME  INSOLUBLE  COMPOUNDS   OF  ZINC.  345 

On  evaporating  a  water  solution  a  part  of  the  chloride 
undergoes  decomposition,  just  as  magnesium  chloride 
does,  forming  the  oxide : 

Zh012  +  H20  =  ZnO  +  2HC1. 

Some  Insoluble  Compounds  of  Zinc. — The  hydroxide, 
sulphide,  carbonate,  and  phosphate  of  zinc  are  insoluble 
in  water. 

EXPERIMENT  160. — Produce  the  insoluble  compounds  just  men- 
tioned and  express  the  reactions  by  means  of  equations.  The 
phosphate  of  zinc  precipitated  by  ordinary  sodium  phosphate  is 
the  normal  phosphate,  Zn3(PC>4)s. 

[What  happens  on  bringing  together  solutions  of  sodium  car- 
bonate and  zinc  sulphate  ?  ammonia  and  zinc  chloride  ?  barium 
chloride  and  zinc  sulphate  ?  lime-water  and  zinc  sulphate  ?  What 
color  has  zinc  sulphide  ?  Is  it  thrown  down  when  the  solution 
contains  dilute  hydrochloric  acid  ?  Try  it .] 


CHAPTER   XXIII. 
THE   COPPER   GROUP:   COPPER,   MERCURY,   SILVER. 

Copper,  Ou  (At.  Wt.  63.6). — Copper  occurs  in  nature 
in  the  uncombined  or  native  state  in  large  quantities  in 
the  neighborhood  of  Lake  Superior  in  the  United  States, 
and  in  China,  Japan,  Siberia,  and  Sweden.  It  also  occurs 
in  combination  with  oxygen  as  ruby  copper,  which  is  the 
oxide  Cu20;  with  sulphur  as  chalcocite,  Cu2S;  and  with 
sulphur  and  iron  in  copper  pyrites,  Cu2S.  Fe2S8. 

Metallurgy. — It  is  obtained  from  the  oxide  by  heating 
it  with  charcoal.  [This  reduction  has  been  illustrated 
under  the  head  of  Carbon  (see  Experiment  88).]  It  is 
also  obtained  from  the  sulphides.  The  chemical  changes 
involved  are  comparatively  complicated.  The  copper 
obtained  in  this  way  contains  impurities  the  nature  of 
which  depends  upon  the  character  of  the  ore  used.  It 
can  be  refined  by  the  electrolytic  method.  For  this  pur- 
pose the  impure  copper  in  thick  plates  is  suspended  in  dilute 
sulphuric  acid  and  connected  with  one  pole  of  a  powerful 
battery.  The  other  pole  is  a  sheet  of  pure  copper.  The 
pure  copper  is  transferred  from  the  plate  of  impure  copper 
to  the  sheet,  while  the  impurities  fall  to  the  bottom  of  the 
tanks.  From  the  mud  thus  collected,  gold,  silver,  and  in 
some  cases  compounds  of  tellurium  are  obtained. 

Properties. — Copper  is  a  hard  metal  of  a  reddish  color 
and  metallic  lustre.  It  does  not  change  in  dry  air,  but  in 

346 


COPPER.  347 

moist  air  it  gradually  becomes  covered  with  a  green  layer 
of  a  carbonate  of  copper.  Nitric  acid  dissolves  it,  copper 
nitrate,  Cu(N03)2,  being  formed,  and  oxides  of  nitrogen 
evolved  [explain  the  reaction] ;  hydrochloric  acid  does  not 
act  upon  it;  sulphuric  acid  acts  when  heated  with  the 
metal;  the  sulphate,  CuS04,  is  formed  and  sulphur  dioxide 
given  off  [explain  the  reaction].  Copper  does  not  decom- 
pose water,  even  when  water-vapor  is  passed  over  the  metal 
heated  to  red  heat.  [Compare  with  the  conduct  of  the 
members  of  the  potassium,  calcium,  and  magnesium 
groups.] 

Dilute  acids  in  general  do  not  act  upon  it  unless  the  air 
has  access  to  it.  This  fact  is  of  importance  in  connection 
with  the  use  of  copper  vessels  in  culinary  operations. 
Substances  containing  vegetable  acids  can  be  boiled  in 
bright  copper  vessels  with  impunity,  for  the  water-vapor 
prevents  access  of  the  air,  but,  on  cooling,  the  air  is 
admitted,  and  then  action  may  take  place,  causing  solution 
of  some  of  the  copper,  which  is  objectionable. 

Precipitation  of  Copper. — Copper  is  precipitated  from 
solutions  of  its  salts  by  zinc,  iron,  and  some  other  metals, 
and  by  an  electric  current. 

EXPERIMENT  161. — In  a  neutral  solution  of  copper  sulphate 
hang  a  strip  of  zinc.  The  zinc  will  become  covered  with  a  layer 
of  copper,  and  zinc  will  pass  into  solution  as  zinc  sulphate.  The 
zinc  simply  displaces  the  copper  in  this  case,  as  it  displaces 
hydrogen  from  sulphuric  acid  : 

Zn  +  CuSO4  =  ZnSO4  +  Cu  ; 
Zn  +  H2SO4  =  ZnSO4  +  H2. 

Perform  a  similar  experiment,  using  a  bright  strip  of  sheet- 
iron  instead  of  the  zinc.  [What  is  the  result  ?]  To  those  who 
first  performed  this  experiment  the  iron  appeared  to  be  changed 
to  copper.  [How  would  you  go  to  work  to  determine  whether  the 
iron  is  changed  to  copper  or  not  ?] 


348  INTRODUCTION   TO  CHEMISTRY. 

Applications.— As  is  well  known,  copper  is  used  very 
extensively  for  a  variety  of  purposes,  among  which  the 
following  may  be  mentioned:  for  electrical  apparatus, 
coins,  copper  vessels,  roofs,  for  covering  the  bottoms  of 
ships,  etc.  It  is  also  used  in  copper-plating;  and  in  the 
preparation  of  a  number  of  valuable  alloys,  such  as  brass, 
bronze,  gun-metal,  bell-metal,  etc. 

Alloys. — Brass  is  a  mixture  or  compound  of  about  one 
part  of  zinc  and  two  parts  of  copper;  these  proportions 
may,  however,  be  varied  between  quite  wide  limits.  There 
is  a  variety  of  brass  containing  equal  parts  of  zinc  and 
copper,  and  another  containing  one  part  of  zinc  and  five 
parts  of  copper.  Pinchbeck  is  made  by  combining  two 
parts  of  copper  and  one  of  brass. 

Bronze  consists  of  copper,  zinc,  and  tin.  The  propor- 
tion of  copper  varies  from  65  to  84  per  cent;  that  of  zinc 
from  31.5  to  11  per  cent;  and  that  of  tin  from  2.5  to 
4  per  cent.  When  exposed  to  the  air  bronze  becomes 
covered  with  a  green  coating  of  basic  copper  carbonate, 
which  protects  it  from  further  action.  This  coating  is  now 
generally  produced  artificially  by  a  variety  of  methods,  as 
by  washing  the  surface  with  a  solution  of  salts  and  acids. 

Gun-metal  consists  generally  of  copper  and  tin  in  the 
proportion  of  11  j>arts  of  tin  and  100*parts  of  copper. 

Bell-metal  contains  a  larger  proportion  (from  20  to  25 
per  cent)  of  tin  than  does  gun-metal. 

Alloys  with  aluminium  containing  aluminium  and 
copper  in  widely  different  proportions  are  made.  That 
with  3  per  cent  of  copper  has  a  whiter  color  than  alumin- 
ium, the  color  being  more  like  that  of  silver.  On  the 
other  hand,  an  alloy  of  copper  with  5  to  10  per  cent  of 
aluminium  has  a  color  resembling  that  of  gold.  This, 
which  is  known  as  aluminium  bronze,  is  very  hard  and 
elastic,  and  is  not  easily  acted  upon  by  chemical  reagents. 


COMPOUNDS   OF  COPPER.  349 

It  is  now  used  to  a  considerable  extent  in  the  manufacture 
of  ornamental  and  useful  articles. 

German  silver  is  an  alloy  consisting  of  copper,  zinc,  and 
nickel. 

Compounds  of  Copper. — Among  the  more  common  com- 
pounds of  copper  are  the  oxides  Cu20  and  CuO;  the  sul- 
phate, CuSO^;  the  carbonate;  and  the  sulphide,  CuS. 

Copper  forms  Two  Series  of  Compounds,— Copper  has 
the  power  to  form  two  distinct  series  of  compounds,  of 
which  the  following  are  examples: 

CuCl,  CuCl2; 

CuBr,          CuBr2; 

Cu20,          CuO. 

Those  compounds  which  are  of  the  first  order,  corre- 
sponding to  the  chloride  CuCl,  are  called  cuprous  com- 
pounds. Thus,  CuCl  is  cuprous  chloride;  Cu20,  cuprous 
oxide,  etc.  On  the  other  hand,  compounds  of  the  second 
order  are  called  cupric  compounds.  Thus,  CuCl2  is  cupric 
chloride;  CuO,  cupric  oxide,  etc.  It  has  been  suggested 
that  perhaps  the  formula  of  the  simpler  cuprous  com- 
pounds like  CuCl,  etc.,  should  be  doubled,  and  written 
Cu2Cl2 ,  Cu2Br2 ,  etc.  This  suggestion  has  its  origin  in  the 
valence  hypothesis.  In  cupric  chloride,  CuCl,,,  and  cupric 
oxide,  CuO,  copper  is  evidently  bivalent;  whereas  if  the 
formulas  of  the  cuprous  compounds  are  the  simple  ones 
CuCl,  CuBr,  etc.,  then  in  them  copper  is  univalent.  If, 
however,  cuprous  chloride  is  Cu^Cl.,,  it  may  be  that  in  it 
the  copper  is  bivalent.  It  is  only  necessary  to  assume  that 
in  the  molecule  of  cuprous  chloride  two  atoms  of  copper 
are  combined  as  represented  thus: 

Cu- 


i, 


35°  INTRODUCTION   TO   CHEMISTRY. 

If  then  each  of  the  copper  atoms  should  combine  with  a 
chlorine  atom,  the  compound  would  have  the  formula 
Cu2Cl2.  Unfortunately,  we  have  no  experimental  means 
of  showing  whether  the  molecule  of  cuprous  chloride  is 
more  probably  Cu2Cl2  or  CuCl,  so  that  the  above  reasoning 
is  purely  speculative.  It  is  better,  therefore,  for  the 
present  to  keep  to  the  simpler  formula.  Whatever  the 
explanation  may  be,  it  is  unquestionably  a  fact  that  there 
are  two  series  of  salts  of  copper,  in  one  of  which  there  is 
relatively  half  as  much  copper  as  in  the  other.  Mercury, 
iron,  and  some  other  metals  present  similar  phenomena. 

Cuprous  oxide,  Cu20,  is  found  in  nature  as  ruby  copper, 
and  is  formed  when  copper  is  heated  in  contact  with  the 
air.  It  is  a  bright-red  substance  insoluble  in  water. 

Cupric  oxide,  CuO,  is  obtained  by  heating  copper  to 
redness  in  contact  with  the  air,  or  by  heating  the  nitrate. 
It  is  also  formed  when  caustic  soda  or  potash  is  added  to 
a  boiling-hot  solution  of  a  copper  salt.  If  the  solution  is 
cold,  blue  cupric  hydroxide,  Cu(OH)2,  is  precipitated,  but 
this  easily  loses  water,  particularly  if  the  solution  is  heated. 
The  reactions  which  take  place  are  : 


CuS04  +  2NaOH  =  Cu(OH)2  +  Na2SO<,  and 
Cu(OH)2  =  CuO  +  H20. 

EXPERIMENT  162.  —  Add  some  caustic  soda  or  potash  to  a  small 
quantity  of  a  cold  solution  of  copper  sulphate  in  a  test-tube. 
Heat  and  notice  the  change  from  blue  to  black. 

Copper  Sulphate,  CuS04  -J-  5H20.  —  This  salt  is  manu- 
factured on  a  large  scale  and  is  commonly  known  by  the 
name  "blue  vitriol."  [What  salt  is  called  "white 
vitriol  "  ?]  It  forms  large  blue  crystals,  and,  when 
heated,  loses  water  and  becomes  colorless.  The  colorless 
substance  becomes  blue  again  in  contact  with  water. 


MERCURY.  35 l 

Copper  sulphate  is  used  extensively  in  the  preparation 
of  blue  and  green  pigments,  in  copper-plating  by  electroly- 
sis, in  galvanic  batteries,  for  preserving  wood,  etc. 

Copper  sulphide,  CuS,  is  a  black  substance  which  is 
formed  by  passing  hydrogen  sulphide  through  a  solution 
of  a  copper  salt,  or  by  adding  a  soluble  sulphide,  as  potas- 
sium sulphide  or  ammonium  sulphide,  to  such  a  solution. 

EXPERIMENT  163. — Treat  a  dilute  solution  of  copper  sulphate 
with  hydrogen  sulphide,  with  ammonium  sulphide,  with  potas- 
sium or  sodium  sulphide. 

Copper-plating. — The  process  of  copper-plating  consists 
in  brief  in  depositing  upon  an  object  a  layer  of  copper  by 
putting  it  in  a  bath  containing  some  copper  salt  and  con- 
necting it  with  one  pole  of  an  electric  battery.  Decom- 
position of  the  copper  salt  takes  place,  and  copper  is 
deposited  upon  the  object.  The  process  is  extensively 
used  in  the  preparation  of  electrotype  plates.  These  are 
prepared  either  from  wood-cuts  or  from  type  by  making  a 
mould  of  plaster  of  Paris,  covering  this  with  graphite,  and 
immersing  the  mould  thus  prepared  in  the  copper-plating 
bath.  The  plate  thus  made  is  an  exact  reproduction  of 
the  wood-cut  or  type  of  which  the  impression  was  taken. 

Mercury,  Hg  (At.  Wt.  200.3). — Mercury  occurs  native 
as  drops  enclosed  in  rocks,  though  principally  in  combina- 
tion with  sulphur  as  cinnabar,  HgS.  It  is  obtained  by 
roasting  cinnabar,  when  vapors  of  mercury  and  sulphur 
dioxide  are  given  off.  The  mercury  is  condensed  in 
appropriate  vessels.  It  is  a  silver-white  metal  of  a  high 
lustre.  At  ordinary  temperatures  it  is  liquid,  though  it 
becomes  solid  at  —  39°. 5.  Its  specific  gravity,  water  being 
the  standard,  is  13.5959.  It  does  not  change  in  the  air  at 
ordinary  temperatures.  It  is  insoluble  in  hydrochloric  acid 


35 2  INTRODUCTION   TO   CHEMISTRY. 

and  cold  sulphuric  acid.  [Try  each.]  It  dissolves  in  hot 
concentrated  sulphuric  acid,  and  is  easily  soluble  in  nitric 
acid.  [Try  each.]  The  vapor  of  mercury  is  very  poison- 
ous. 

Uses, — Mercury  is  extensively  used  in  the  manufacture 
of  thermometers,  barometers,  etc. ;  as  tin  amalgam  for 
mirrors;  and  in  the  processes  by  which  gold  and  silver  are 
obtained  from  their  ores. 

Amalgams. — With  other  metals  it  forms  alloys  called 
amalgams.  In  ordinary  galvanic  batteries  the  zinc  plates 
are  treated  with  mercury,  and  thus  covered  with  a  layer  of 
zinc  amalgam  which  protects  them  from  the  action  of  the 
acids  used. 

Compounds  of  Mercury. — Among  the  more  common 
compounds  of  mercury  are  the  oxide,  HgO;  the  two 
chlorides,  mercurous  chloride,  HgCl,  and  mercuric  chloride, 
HgCl2;  the  two  iodides,  mercurous  iodide,  Hgl,  and  mer- 
curic iodide,  HgI2 ;  and  the  sulphide,  HgS. 

Mercuric  oxide,  HgO,  is  the  red  substance  which  was 
used  in  one  of  our  first  experiments  for  the  purpose  of 
preparing  oxygen.  It  was  by  heating  this  substance  that 
oxygen  was  discovered,  and  the  discovery  of  oxygen  is  per- 
haps the  most  important  event  in  the  history  of  chemistry. 
It  is  formed  when  mercury  is  heated  for  some  time  near  its 
boiling-point  in  contact  with  the  air,  and  is  made  by  heat- 
ing the  nitrate. 

. 

Mercurous  chloride,  HgCl,  is  commonly  known  by  the 
name  calomel.  It  is  precipitated  when  a  soluble  chloride 
or  hydrochloric  acid  is  added  to  a  solution  of  any  mercu- 


COMPOUNDS  OF  MERCURY.          353 

rous  salt.  It  is  manufactured  by  subliming  an  intimate 
mixture  of  mercuric  chloride  and  mercury: 

HgCl,  +  Hg  =  2HgCI. 

It  is  a  white  substance,  insoluble  in  water,  which  finds  ex- 
tensive application  in  medicine. 

Mercuric  chloride,  HgCl2,  commonly  called  corrosive 
sublimate,  is  manufactured  on  the  large  scale  by  subliming 
an  intimate  mixture  of  mercuric  sulphate  and  common 
salt: 

HgSO,  -j-  SNaCl  =  Na2S04  +  HgCl2. 

It  is  a  white  substance,  soluble  in  water.  It  is  extremely 
poisonous.  It  has  a  very  marked  influence  upon  the  lower 
organisms  that  play  so  important  a  part  in  producing  dis- 
ease and  the  decay  of  organic  substances.  Wood  im- 
pregnated with  it  is  partly  protected  from  decay.  In 
surgery  it  is  used  for  the  purpose  of  preventing  contamina- 
tion of  wounds  by  the  hands  and  instruments  of  the 
surgeon. 

Mercuric  sulphide,  HgS,  occurs  in  nature  as  cinnabar 
in  the  form  of  red  crystals  or  crystalline  masses.  When 
prepared  artificially  by  rubbing  mercury  and  flowers  of 
sulphur  together,  or  by  passing  hydrogen  sulphide  through 
a  solution  containing  a  mercury  salt,  it  is  a  black  powder. 
When  sublimed  this  powder  yields  red  crystals. 

Precipitation  of  Mercury  as  Mercurous  Chloride. — It  will 
be  noticed  that  of  the  two  chlorides  only  mercurous 
chloride  is  insoluble  in  water.  If  any  mercurous  salt  is 
present  in  a  solution,  mercurous  chloride  will  be  thrown 
down  on  adding  a  chloride  or  hydrochloric  acid;  whereas 
if  the  solution  contains  a  mercuric  salt  the  addition  of  a 
chloride  or  hydrochloric  acid  will  produce  no  precipitate. 


354  INTRODUCTION   TO  CHEMISTRY. 

Silver,  Ag  (At.  Wt.  107.93).— Silver  occurs  native;  in 
combination  with  sulphur;  and  with  sulphur  and  other 
metals.  Small  quantities  of  silver  sulphide  are  found  in 
almost  all  varieties  of  galenite  or  lead  sulphide.  It  occurs 
more  rarely  as  the  chloride,  bromide,  and  iodide. 

Metallurgy  of  Silver. — Much  of  the  silver  in  use  is 
obtained  from  galenite,  PbS.  This  mineral  is  treated  in 
such  a  way  as  to  cause  the  separation  of  the  lead  (which 
see),  and  the  silver  is  separated  from  sulphur  at  the  same 
time.  But  it  is  dissolved  in  a  large  quantity  of  lead,  and 
the  problem  that  presents  itself  to  the  metallurgist  is  how 
to  separate  the  small  quantity  of  silver  from  the  large 
quantity  of  lead. 

Pattinson's  Method. — This  is  accomplished  by  melting 
the  mixture  and  allowing  it  to  cool  until  crystals  appear. 
These  are  almost  pure  lead.  They  are  dipped  out  by 
means  of  a  sieve-like  ladle,  and  the  liquid  left  is  again 
allowed  to  stand,  when  crystals  are  again  formed,  and  these 
are  removed  in  the  same  way  as  before.  By  this  means, 
and  by  again  melting  the  crystals  removed,  allowing  the 
liquid  to  crystallize,  and  removing  the  crystals  formed, 
there  is  finally  obtained  a  product  rich  in  silver,  but  which 
still  contains  lead.  This  is  heated  in  appropriate  vessels 
in  contact  with  the  air,  when  the  lead  is  oxidized,  while 
the  silver  remains  in  the  metallic  state.  This  method  of 
concentrating  by  crystallization  of  lead  is  known  as  Pat- 
tinson's Method.  This  process  has  been  superseded  by  the 

Zinc  Method,  or  Parkes's  Method. — This  consists  in 
treating  the  molten  alloy  with  zinc,  which  takes  up  all  the 
silver,  and  the  alloy  of  zinc  and  silver  thus  formed  is 
removed,  and  afterwards  treated  with  superheated  steam, 
by  which  the  zinc  is  oxidized  and  the  silver  left  unchanged. 


SILYER.  355 

Amalgamation  Process, — Some  ores  of  silver  are  treated 
in  another  way,  known  as  the  amalgamation  process.  The 
ores  are  mixed  with  common  salt  and  roasted,  when  the 
silver  is  obtained  in  the  form  of  the  chloride.  This  is  then 
reduced  to  silver  by  means  of  iron  and  water,  the  reaction 
taking  place  as  represented  in  the  following  equation : 

2AgCl  +  Fe  =  FeCl2  +  2Ag. 

The  mixture  is  next  treated  with  mercury,  which  forms 
an  amalgam  with  the  silver,  while  the  other  metals  present 
do  not  combine  with  the  mercury.  The  amalgam  can  be 
separated  from  the  rest  of  the  mass  without  difficulty,  and 
when  heated  to  a  sufficiently  high  temperature  the  mercury 
distils  over,  leaving  the  silver. 

Refining  of  Silver. — Silver  is  refined  by  either  of  two 
methods : 

1.  The  Sulphuric  Acid  Method. — In  this  the  crude  metal 
is  dissolved  in  sulphuric  acid  when  gold  and  other  valuable 
metals  remain  undissolved.     From  the  solution  of  the  sul- 
phate the  silver  is  precipitated  by  metallic  iron.     It  comes 
down  in  finely-divided  form.     This  is  pressed  into  bricks, 
and  melted  down. 

2.  The  Electrolytic   Method.  —  This   is   similar   to   the 
process  used  for  copper. 

Properties. — Silver  is  a  white  metal  with  a  high  lustre. 
It  is  not  acted  upon  by  air,  oxygen,  or  water.  Sulphur 
acts  upon  it  readily,  forming  a  black  coating  of  silver  sul- 
phide. The  metal  is  not  dissolved  by  hydrochloric  acid, 
but  is  easily  dissolved  by  concentrated  sulphuric  acid  and 
by  dilute  nitric  acid. 

Alloys  of  Silver. — The  silver  used  for  coins  and  most 
other  purposes  is  an  alloy  with  copper,  the  pure  metal 


35 6  INTRODUCTION   TO   CHEMISTRY. 

being  too  soft.  The  alloy  usually  contains  from  7-J  to  10 
per  cent  of  copper.  Other  metals  covered  with  a  layer  of 
silver,  deposited  by  the  action  of  an  electric  battery,  are 
said  to  be  silver-plated. 

Compounds  of  Silver. — The  principal  compounds  of 
silver  are  the  chloride,  AgCl;  bromide,  AgBr;  iodide,  Agl; 
and  nitrate,  AgN03. 

Silver  nitrate,  AgN03,  is  known  also  by  the  name 
"lunar  caustic."  It  is  prepared  by  dissolving  silver  in 
dilute  nitric  acid. 

EXPERIMENT  164. — Dissolve  a  10-  or  a  25-cent  piece  in  dilute 
nitric  acid.  [What  action  takes  place  ?]  Dilute  the  solution 
to  200-300  cc.  with  water.  [What  is  the  color  of  the  solution  ? 
What  does  this  indicate  ?  Does  this  color  prove  the  presence  of 
copper  ?]  Add  a  solution  of  common  salt  until  it  ceases  to  pro- 
duce a  precipitate.  [What  is  the  chemical  change  ?]  Filter  off 
the  white  silver  chloride  and  carefully  wash  with  hot  water. 
Dry  the  precipitate  on  the  filter,  by  placing  the  funnel  with  the 
filter  and  precipitate  in  an  air-bath  heated  to  about  100°.  Re- 
move the  precipitate  from  the  filter  and  put  it  into  a  porcelain 
crucible.  Heat  gently  with  a  small  flame  until  the  chloride  is 
melted.  Cut  out  a  piece  of  sheet-zinc  large  enough  to  cover  the 
bottom  of  the  crucible,  and  lay  it  on  the  silver  chloride.  Now 
add  a  little  water  and  a  few  drops  of  dilute  sulphuric  acid,  and 
let  the  whole  stand  for  twenty-four  hours.  The  silver  chloride  is 
reduced  to  silver,  and  zinc  chloride  is  formed  : 

Zn  +  SAgCl  =  ZnCla  +  2Ag. 

Take  out  the  piece  of  zinc  and  wash  the  silver  with  a  little 
dilute  sulphuric  acid,  and  then  with  water.  Heat  a  small  piece 
of  the  metal  on  charcoal  in  the  blowpipe  flame  until  it  melts 
and  forms  a  bead.  Dissolve  the  silver  in  dilute  nitric  acid  and 
evaporate  to  dryness  on  a  water-bath,  so  that  the  excess  of  nitric 
acid  is  driven  off.  Dissolve  the  residue  in  water  and  put  the 
solution,  either  in  a  bottle  of  dark  glass  or  in  one  wrapped  in 
dark  paper. 


COMPOUNDS   OF  SILVER  IN  PHOTOGRAPHY.        357 

EXPERIMENT  165. — To  a  few  cubic  centimetres  of  water  in  a 
test-tube  add  5  to  10  drops  of  the  solution  of  silver  nitrate  just 
prepared.  To  this  dilute  solution  add  a  little  of  a  dilute  solution 
of  sodium  chloride.  The  curdy  white  precipitate  is  silver  chloride. 
Stand  it  aside  where  the  light  can  shine  upon  it,  and  notice  the 
change  of  color  which  gradually  takes  place.  In  the  same  way 
make  the  bromide  by  adding  potassium  bromide,  and  the  iodide 
by  adding  potassium  iodide,,  to  silver  nitrate. 

Application  of  Compounds  of  Silver  in  Photography,— 

It  will  be  seen  from  the  last  experiments  that  the  chloride, 
bromide,  and  iodide  of  silver  are  insoluble  in  water  and  are 
changed  by  light.  The  art  of  photography  is  based  upon 
the  changes  that  certain  compounds,  especially  salts  of 
silver,  undergo  when  exposed  to  the  light.  Silver  iodide 
is  best  adapted  to  most  purposes.  The  salt  is  so  changed 
by  the  light  that  when  treated  with  certain  compounds, 
such  as  ferrous  sulphate,  pyrogallic  acid,  etc.,  called 
"  developers,"  a  deposit  of  finely-divided  silver  is  formed 
upon  the  plate  in  those  places  affected  by  the  light.  A 
plate  of  glass,  or  a  sheet  of  properly-prepared  paper,  is 
covered  in  the  dark  with  a  thin  layer  of  a  salt  of  silver. 
The  plate  is  then  exposed  in  the  camera  to  the  action  of 
the  light  from  some  object  to  be  photographed.  The  salt 
is  changed  where  it  is  acted  upon  by  the  light,  while  where 
there  is  no  light  it  is  not  acted  upon.  An  image  of  the 
object  towards  which  the  plate  was  directed  is  thus  left  on 
the  plate.  But  after  the  action  of  the  developer  is  com- 
plete there  is  still  upon  the  plate  unchanged  silver  salt. 
To  remove  this  the  plate  is  washed  with  a  solution  of 
sodium  thiosulphate,  Na2S203  (hyposulphite),  which  dis- 
solves the  salt. 

Precipitation  of  Metallic  Silver, — Silver  is  precipitated 
from  solutions  of  its  salts  by  zinc,  copper,  mercury,  and 
other  metals. 


358  INTRODUCTION   TO   CHEMISTRY. 

EXPERIMENT  166.— To  a  solution  of  silver  nitrate  containing 
about  5  grams  of  the  salt  in  100  cc.  water  add  a  few  drops  of 
mercury,  and  let  it  stand.  In  a  few  days  the  silver  will  be  de- 
posited in  the  form  of  delicate  crystals.  This  formation  is  called 
the  "  silver-tree." 

Insoluble  Compounds  of  Silver. — The  oxide,  chloride, 
bromide,  iodide,  sulphide,  carbonate,  and  phosphate  of 
silver  are  insoluble  in  water. 

EXPERIMENT  167.— Verify  this  statement.  [What  takes  place 
when  hydrochloric  acid  is  added  to  a  solution  of  a  silver  salt  ? 
When  silver  nitrate  is  added  to  barium  chloride  ?  "When  ammo- 
nium carbonate  is  added  to  silver  nitrate  ?  When  disodium  phos- 
phate is  added  to  silver  nitrate?  In  this  case,  normal  silver 
phosphate,  Ag3PO4 ,  is  formed  and  some  nitric  acid  is  set  free.] 

Argentous  and  Argentic  Compounds. — Silver  generally 
forms  compounds  that  are  analogous  to  the  cuprous  and 
mercurous  salts,  and  not  those  which  are  analogous  to  the 
cupric  and  mercuric  salts.  There  is,  however,  an  oxide, 
Ag20,  and  another,  AgO,  corresponding  to  mercurous  and 
mercuric  oxides. 

The  Specific  Heat  of  Elements  as  a  Means  of  Determin- 
ing their  Atomic  Weights. — The  question  naturally  sug- 
gests itself,  How  are  the  atomic  weights  determined  in  the 
case  of  elements  like  silver,  copper,  etc.,  which  cannot  he 
converted  into  the  form  of  vapor,  and  which  do  not  yield 
compounds  that  can  be  converted  into  vapor  ?  It  will  be 
remembered  that  most  of  the  atomic  weights  with  which 
we  have  thus  far  had  to  deal,  as  those  of  oxygen,  chlorine, 
nitrogen,  etc.,  are  determined  by  a  consideration  of  the 
specific  gravity  of  the  vapors  of  the  compounds  of  these 
elements.  The  relative  weights  of  equal  volumes  of  these 
gases  or  vapors  are  determined,  and  then,  assuming  that 
these  weights  express  the  relative  weights  of  the  molecules 
of  the  compounds,  the  smallest  weight  of  the  element 


SPECIFIC  HEAT  OF  ELEMENTS.  359 

occurring  in  any  compound  is  selected  as  the  atomic 
weight.  [Refer  back  and  carefully  read  the  chapter  relat- 
ing to  the  Atomic  Theory  and  Avogadro's  Hypothesis.] 
But  however  valuable  this  method  may  be,  it  does  not 
help  us  in  the  case  of  those  elements  which  do  not  yield 
compounds  capable  of  conversion  into  vapor.  In  such 
cases  the  effect  of  heat  upon  the  elements  is  of  assistance. 
It  has  been  found  that  when  equal  weights  of  different 
elements  are  exposed  to  exactly  the  same  source  of  heat, 
they  require  different  lengths  of  time  to  become  heated  to 
the  same  temperature.  Given  exactly  the  same  heating 
power,  a  pound  of  water  must  be  heated  about  32  times 
as  long  to  raise  its  temperature  10,  20,  or  30  degrees  as  a 
pound  of  mercury  must  be  heated  to  raise  its  temperature 
the  same  number  of  degrees;  or  it  takes  about  32  times  as 
much  heat  to  raise  a  pound  of  water  10,  20,  or  30  degrees 
as  it  does  to  raise  a  pound  of  mercury  the  same  number 
of  degrees.  The  quantity  of  heat  required  to  raise  the 
temperature  of  a  certain  weight  of  a  substance  one  degree 
as  compared  with  the  quantity  of  heat  required  to  raise  the 
temperature  of  the  same  weight  of  water  one  degree  is 
called  the  specific  heat  of  the  substance.  Thus,  from  what 
was  said  above,  the  specific  heat  of  mercury  is  nearly  J^, 
or,  in  decimals,  0.0319.  In  a  similar  way  it  can  be  shown 
that  the  specific  heat  of  gold  is  0.0324;  of  zinc,  0.0955; 
of  silver,  0.057;  of  copper,  0.0952.  But  these  figures 
bear  a  remarkable  relation  to  the  atomic  weights  found  by 
means  of  analysis.  Thus,  taking  the  above  elements,  we 
have: 

Specific  Heat.  At.  Weight 

Mercury 0.0319  200.3 

Gold 0.0324  197.2 

Zinc 0.0955  65.4 

Silver 0.057  107.93 

Copper 0.0952  63.6 


360  INTRODUCTION    TO   CHEMISTRY. 

Calculation  will  show  that  the  specific  heat  of  these  ele- 
ments is  approximately  inversely  proportional  to  their 
combining  weights.  Thus, 

0.0319        :         0.057        ::       107.93          :         200.3. 

Sp.  Ht.  of  Hg.          Sp.  Ht.  of  Ag.  At.  Wt.  of  Ag.  At.  Wt.  of  Hg. 

And  the  same  is  true  in  the  other  cases.  Or  the  relation 
maybe  stated  in  another  way,  viz.:  The  product  of  the 
specific  heat  of  any  element  multiplied  by  its  combining 
weight  is  the  same  in  all  cases.  The  product  is  about 
6.25.  It  is  believed  that  the  quantities  of  the  elements  to 
which  this  law  refers  are  in  reality  the  atomic  weights,  and 
we  therefore  accept  the  law  known  as  the  law  of  Dulong 
and  Petit,  which  is  this: 

The  atomic  weight  of  an  element  multiplied  ~by  its  specific 
heat  is  a  constant  which  has  a  value  of  about  6.25. 

There  are  some  exceptions  to  the  law,  but  these  cannot 
be  discussed  at  this  time.  Despite  its  imperfections  it  is 
now  recognized  as  furnishing  a  valuable  means  of  deter- 
mining atomic  weights.  If  A  represents  the  atomic 
weight,  and  S  the  specific  heat,  then,  according  to  the  law 

6  25 
of  Dulong  and  Petit,  A  X  S  =  6.25  nearly,  and  A  —  -^— . 

h 

To  determine  the  atomic  weight  of  an  element  by  this 
method,  then,  it  is  only  necessary  to  determine  the  specific 
heat  of  the  element.  Substituting  for  S  the  figure  found, 
the  value  of  A  can  be  easily  calculated.  By  careful  analy- 
sis of  compounds  of  the  element  the  figure  can  be  deter- 
mined more  accurately. 


CHAPTER   XXIV. 

THE   ALUMINIUM    GROUP: 

ALUMINIUM,  GALLIUM,  INDIUM,    THALLIUM,     SCAN- 
DIUM,  YTTRIUM,    LANTHANUM,   AND   YTTERBIUM. 

General. — The  only  element  of  this  group  that  need  be 
treated  here  is  aluminium.  This  is  an  extremely  impor- 
tant element  that  is  found  very  widely  distributed  in 
nature. 

Aluminium,  Al  (At.  Wt.  27.1). — Among  the  many  im- 
portant and  widely-distributed  minerals  that  contain 
aluminium  are  feldspar,  granite,  mica,  and  cryolite. 

Feldspar  is  a  silicate  of  aluminium  and  potassium  of  the 
formula  AlKSi308.  Mica  is  a  general  name  applied  to  a 
large  number  of  minerals  which  are  silicates  of  aluminium 
and  some  other  metal,  as  potassium,  lithium,  magnesium, 
etc.  The  simplest  form  of  mica  is  that  represented  by  the 
formula  K AlSi04 ,  according  to  which  the  mineral  is  a  salt 
of  orthosilicic  acid,  Si(OH)4.  Cryolite  is  a  double  fluoride 
of  aluminium  and  sodium,  or  the  sodium  salt  of  fluo- 
aluminic  acid,  Na3AlF6.  Bauxite  is  a  hydroxide  of 
aluminium  in  combination  with  a  hydroxide  of  iron. 
Aluminium  occurs  in  the  products  of  decomposition  of 
minerals,  as  well  as  in  the  above  forms.  One  of  the  most 
important  of  these  is  clay,  which  is  found  in  all  conditions 
of  purity,  from  white  kaolin  to  ordinary  dark-colored  clay. 
Kaolin  is  the  aluminium  salt  of  orthosilicic  acid  of  the 

361 


362  INTRODUCTION   TO   CHEMISTRY. 

formula  Al4(Si04)3  -f-  4H20.  Aluminium  silicate  is  found 
in  all  soils,  but  is  not  taken  up  by  plants,  and  does  not  find 
entrance  into  tbe  animal  body.  The  name  aluminium  has 
its  origin  in  the  fact  that  alum  was  known  at  an  early  date, 
and  the  metal  was  afterwards  isolated  from  it. 

Preparation. — The  preparation  of  aluminium  on  the 
large  scale  is  an  important  problem.  The  element  has 
properties  which  would  appear  to  adapt  it  to  most  uses  to 
which  iron  is  put,  and  for  many  purposes  it  has  advantages 
over  iron.  Further,  nature  supplies  us  with  unlimited 
quantities  of  the  compounds  of  aluminium,  which  are  dis- 
tributed everywhere  over  the  earth.  While,  however,  iron, 
lead,  tin,  copper,  and  other  metals  can  be  isolated  from 
their  natural  compounds  without  serious  difficulty,  alu- 
minium, which  is  more  abundant  than  any  of  them,  and  in 
some  respects  more  valuable  than  any  of  them,  is  locked 
in  its  compounds  so  firmly  that  it  cannot  be  as  readily 
obtained. 

It  is  best  prepared  by  electrolysis.  The  most  economical 
method  consists  in  passing  an  electric  current  through  a 
bath  of  molten  cryolite  containing  aluminium  oxide  in  the 
form  of  corundum  in  solution.  Iron  pots  are  used.  These 
form  one  electrode,  while  carbon  rods  are  used  for  the  other 
electrode. 

Properties. — The  color  of  aluminium  is  like  that  of  tin, 
and  it  has  a  high  lustre.  It  is  very  strong,  and  yet 
malleable.  It  is  lighter  than  most  metals  in  common  use, 
its  specific  gravity  being  2.5  to  2.7  according  to  the  con- 
dition, while  that  of  iron  is  7.8,  that  of  silver  10.57,  that 
of  tin  7.3,  and  that  of  lead  11.37.  It  does  not  change  in 
dry  or  in  moist  air;  and  in  the  compact  form  it  does  not 
act  upon  water  even  at  elevated  temperatures.  It  melts 
at  about  700°,  which  is  higher  than  the  melting-point  of 


ALUMINIUM.  363 

zinc,  and  lower  than  that  of  silver.  Hydrochloric  acid 
dissolves  it  with  ease,  forming  aluminium  chloride.  At 
ordinary  temperatures  nitric  and  sulphuric  acids  do  not 
act  upon  it;  ,at  higher  temperatures,  however,  action  takes 
place,  and  the  corresponding  salts  are  formed.  It  dis- 
solves in  solutions  of  the  caustic  alkalies,  forming  the 
so-called  aluminates.  It  reduces  many  oxides  when  heated 
with  them  to  a  high  temperature;  and  it  is  used  in  the 
preparation  of  boron  and  silicon. 

Applications. — The  metal  is  used  to  a  considerable 
extent  in  the  preparation  of  ornaments,  and  of  useful 
articles  in  which  lightness  is  of  importance,  as  in  tele- 
scopes and  opera-glasses.  An  alloy  with  a  small  percentage 
of  silver  is  used  for  the  beams  of  chemical  balances. 
Aluminium  bronze,  which  is  an  alloy  with  copper,  is  also 
used  quite  extensively.  (See  under  Copper.)  Magnalium 
is  an  interesting  alloy  of  aluminium  with  magnesium. 

High  temperatures  (about  3000°  C.)  are  attained  by 
burning  cartridges  containing  a  mixture  of  aluminium  and 
ferric  oxide.  Practical  use  is  made  of  this  process  in 
welding. 

Compounds  of  Aluminium. — Among  the  more  important 
compounds  of  aluminium  are  the  oxide,  A1203;  the  hy- 
droxide, A1(OH)3;  the  alums;  the  silicates;  and  the 
chloride,  A1C13. 

Aluminium  Oxide,  A1203. — This  compound  occurs  in 
nature  in  the  form  of  ruby,  sapphire,  and  corundum.  It 
is  very  hard,  and  as  emery  is  used  for  polishing.  It  is 
made  artificially  by  heating  the  hydroxide,  A1(OH)3: 

2A1(OH)3  =  A1203  +  3H20. 

Aluminium  Hydroxide,  A1(OH)5. — This  compound  is 
found  in  nature  in  crystallized  form  as  hydiargillite.  It 


364  INTRODUCTION  TO  CHEMISTRY. 

is  precipitated  when  ammonia  is  added  to  a  solution  of. 
aluminium  sulphate: 


A12(S04)3  +  GNH.OH  =  3(NH4)2S04  +  2A1(OH)8. 

It  forms  a  gelatinous  mass  which  it  is  difficult  to  filter. 
[Precipitate  some  from  a  solution  of  ordinary  alum.]  The 
hydroxide  is  soluble  in  acids  and  in  alkalies.  In  the 
former  case  salts  are  formed  in  which  the  hydroxide  plays 
the  part  of  a  base;  in  the  latter  it  acts  like  an  acid.  The 
salts  formed  with  the  alkalies  are  called  aluminaf.es.  In 
aluminium  salts  oii«  atom  of  the  metal  replaces  three  atoms 
of  hydrogen;  thus,  aluminium  nitrate  is  A1(N03)3;  the 
sulphate,  A12(S04)3  ,  etc.  In  the  aluminates  the  three 
hydrogen  atoms  of  the  hydroxide  are  replaced  by  metal; 
thus,  potassium  aluminate  is  A1(OK)3,  and  sodium  alumi- 
nate  Al(ONa)8. 

EXPERIMENT  168.  —  Precipitate  some  aluminium  hydroxide  from 
a  dilute  solution  of  alum,  by  means  of  caustic  potash,  and  con- 
tinue to  add  the  latter  slowly,  when  the  precipitate  will  dissolve. 
Do  the  same  with  caustic  soda. 

•Aluminium  hydroxide,  A1(OH.)3,  loses  water  when 
heated,  and  a  compound  of  the  formula  A102H  is  formed  : 

A1(OH)3  =  A102II  +  H20. 

This  compound  is  found  in  nature  as  the  mineral 
diaspore.  It  has  acid  properties  and  forms  extremely 
stable  salts,  several  of  which  are  found  in  nature.  Spinel 
is  magnesium  aluminate  (A102)2Mg.  The  formation  of 
the  hydroxides  A1(OH)3  and  A102H,  and  of  salts  derived 
from  each,  indicates  some  analogy  between  aluminium  and 
boron.  On  the  other  hand,  the  power  to  replace  the 
hydrogen  of  acids  is  not  possessed  by  boron  to  any  great 
extent.  [Refer  back  to  Boron.  Read  again  what  is  said 
about  it,  and  compare  it  with  aluminium.] 


COMPOUNDS  OF  ALUMINIUM.  365 

Alums. — With  the  sulphates  of  the  alkali  metals  alumin- 
ium sulphate  forms  complex  compounds  which  crystallize 
beautifully.  Potassium  alum  is  the  best  known  of  these. 
It  ma.y  be  regarded  as  derived  from  2  molecules  of  sul- 
phuric acid  by  the  replacement  of  3  atoms  of  hydrogen  by 
1  atom  of  aluminium,  and  the  fourth  by  1  atom  of  potas- 
sium; thus,  A1K(SOJ2.  The  crystals  always  contain  12 
molecules  of  water,  the  complete  formula  being  AlK(SOJa 
-f  12H20.  Similarly,  sodium  alum  is  AlNa(SOJ2  -f 
12H20,  and  ammonium  alum  A1NH4(S04)2  -f  12H20. 

EXPERIMENT  169. — Determine  whether  the  alum  in  the  labora- 
tory contains  potassium  or  ammonium.  Crystallize  some.  What 
forms  do  the  crystals  possess  ? 

Aluminium  Silicate. — The  silicate  of  aluminium  occurs 
in  nature  in  enormous  quantities.  The  most  important 
of  the  minerals  containing  it  are  the  feldspars,  of  which 
ordinary  feldspar,  KAlSi308 ,  is  the  most  abundant.  .  The 
feldspars,  again,  enter  into  the  composition  of  granite 
together  with  quartz  and  mica,  and  mica  itself  is  a  double 
silicate  of  aluminium. 

Natural  Decomposition  of  Feldspar. — Under  the  influ- 
ence of  moisture,  the  carbon  dioxide  of  the  air,  and 
changes  in  temperature,  the  feldspars  are  undergoing  slow 
decomposition,  the  products  being  mainly  potassium  or 
sodium  silicate  and  aluminium  silicate.  The  salts  of  the 
alkali  metals,  principally  the  potassium  salt,  being  soluble, 
are  carried  away,  and  find  their  way  into  the  soil.  The 
silicate  of  aluminium  is  not  soluble,  but  it  easily  forms  an 
emulsion  with  water,  and  is  therefore  carried  down  the 
sides  of  the  hills  and  mountains  upon  which  it  is  formed 
into  the  valleys,  and  much  of  it  finds  its  way  into  streams. 
Sometimes  this  carrying  away  is  prevented,  and  then  beds 
of  comparatively  pure  clay,  known  as  kaolin,  are  formed. 


3^6  INTRODUCTION   TO  CHEMISTRY. 

The  clay  found  in  the  valleys  is  always  more  or  less  impure 
and  colored. 

Kaolin. — This  is  the  purest  form  of  aluminium  silicate 
found  in  nature.  It  always  contains  water.  Its  composi- 
tion varies,  some  specimens  on  analysis  giving  results 
which  lead  to  the  formula  Al4(Si04)s  -)-  4H20,  according 
to  which  the  substance  is  the  salt  of  normal  silicic  acid 
Si(OH)4.  Other  specimens  have  the  composition  HAlSi04 
-j-  H20.  When  heated  alone  kaolin  does  not  melt;  but  if 
feldspar  is  added  to  it,  the  whole  melts,  and  forms  a 
translucent  mass  known  as  porcelain.  Other  substances 
besides  feldspar  may  be  used  for  this  purpose. 

Clay. — Ordinary  clay,  as  has  been  stated,  is  a  name 
given  to  the  impure  varieties  of  aluminium  silicate  which 
have  been  carried  down  from  the  place  of  formation. 
Among  the  substances  besides  aluminium  silicate  found  in 
clays  are  calcium  carbonate,  magnesium  carbonate,  sand, 
and  hydroxides  of  iron.  The  color  is  largely  determined 
by  the  amount  of  the  hydroxides  of  iron  present.  The 
better  varieties  are  used  in  the  manufacture  of  the  so-called 
"  stone-ware,"  gas-retorts,  and  fire-bricks.  The  colored 
varieties  are  used  in  making  ordinary  earthenware  and 
bricks.  Marl  is  clay  mixed  with  considerable  quantities 
of  calcium  carbonate. 

Ultramarine. — The  substance  occurring  in  nature  and 
known  as  lapis  lazuli  consists  of  a  silicate  of  sodium  and 
aluminium  together  with  a  sulphur  compound,  probably  a 
polysulphide  of  sodium.  The  coloring  matter,  known  as 
ultramarine,  obtained  by  powdering  it  was  formerly  very 
expensive,  but  it  is  now  made  artificially  by  the  ton,  and 
the  color  of  the  artificially-prepared  substance  is  even  more 
beautiful  than  that  of  the  natural.  The  artificial  prepara- 


PORCELAIN,  367 

tion  is  effected  by  melting  together  kaolin,  anhydrous 
sodium  carbonate,  and  sulphur;  or  clay,  calcined  sodium 
sulphate,  and  charcoal.  By  varying  the  conditions  of 
preparation,  products  of  different  colors  are  obtained. 
Besides  the  deep-blue  ultramarine,  there  are  now  manu- 
factured ultramarines  of  different  shades  of  blue,  and  a 
green  variety. 

Ultramarine  is  now  manufactured  in  very  large  quantity 
— according  to  a  recent  report,  to  the  extent  of  nearly  9000 
tons  a  year.  It  is  the  most  extensively  used  blue  coloring 
matter. 

Porcelain, — It  was  stated  above  that  when  kaolin  is 
heated  alone  it  does  not  melt,  but  that  if  feldspar  is  added 
to  it,  or  if  that  found  in  nature  contains  feldspar,  as  is 
frequently  the  case,  it  either  fuses  together  forming  a  com- 
pact mass,  or  melts  and  forms  a  translucent  mass. 
Further,  when  kaolin  or  any  other  variety  of  clay  is  mixed 
with  water,  a  plastic  substance  results,  which  can  be 
kneaded  and  worked  into  any  desired  form.  These  facts 
form  the  basis  of  the  manufacture  of  earthenware,  porce- 
lain, etc.  The  ease  with  which  the  mass  melts  depends 
upon  the  quantity  of  feldspar  or  other  flux  added  to  it. 
If  but  little  is  added  it  melts  with  difficulty;  if  much  is 
added  it  melts  easily. 

In  the  manufacture  of  the  finest  kinds  of  porcelain 
kaolin  is  used.  This  is  generally  mixed  with  a  little  feld- 
spar or  chalk>  gypsum,  or  some  other  flux,  and  sand  is  also 
added.  All  these  substances  must  be  very  finely  ground. 
The  mixture  is  then  worked  into  the  desired  forms,  and 
carefully  dried.  After  the  objects  are  dried  they  are 
burned,  first  at  a  red  heat  at  which  the  mass  becomes 
solid,  afterwards  at  a  white  heat  for  the  purpose  of  form- 
ing a  glaze  upon  the  surface.  The  product  after  the  first 
burning  is  that  which  is  familiar  as  porous  earthenware; 


368  INTRODUCTION   TO   CHEMISTRY. 

that  formed  in  the  second  burning  is  the  porcelain  with 
glaze  as  it  is  commonly  used. 

In  order  to  form  the  glaze  upon  the  porcelain  the 
porous  earthenware  first  formed  is  drawn  through  a  vessel 
containing  proper  materials  in  finely-powdered  condition 
and  suspended  in  water.  The  materials  used  are  generally 
the  same  as  those  used  for  the  porcelain  itself,  but  they 
are  mixed  in  different  proportions,  with  less  kaolin  and 
more  sand  and  feldspar,  so  as  to  be  more  easily  fusible. 
After  this  treatment  the  objects  are  again  heated  to  a  high 
temperature. 

Earthenware, — The  ordinary  varieties  of  earthenware 
are  made  from  clays  which  are  much  less  pure  than  kaolin. 
Ordinary  colored  clay  is  used.  The  objects  are  formed, 
and  then  subjected  in  general  to  the  same  kind  of  treat- 
_ment  as  porcelain.  They  are  glazed  in  different  ways. 
One  method  consists  in  bringing  the  glazing  material  on 
the  earthenware  before  it  is  burned ;  another  method  con- 
sists in  putting  the  objects  in  the  furnace  without  a  glaze, 
and  towards  the  end  of  the  firing  process  sodium  chloride 
is  thrown  into  the  furnace,  and  is  thus  brought  in  contact 
with  the  ware  in  the  form  of  vapor.  A  chemical  change 
takes  place,  resulting  in  the  formation  of  a  silicate  of 
aluminium  and  sodium  upon  the  surface.  This  melts,  and 
forms  a  glaze. 

Bricks  are  the  most  common  variety  of  unglazed  earthen- 
ware. Owing  to  1he  presence  of  other  substances  besides 
aluminium  silicate,  as,  for  example,  calcium  carbonate, 
the  material  is  comparatively  easily  fusible.  The  color  of 
red  bricks  is  largely  due  to  the  presence  of  oxides  of  iron. 

Action  of  Soluble  Carbonates  and  Soluble  Sulphides  on 
Solutions  of  Aluminium  Salts. — With  weak  acids  alumin- 
ium forms  no  salts.  There  is,  for  example,  no  carbonate. 


REACTIONS   OF  ALUMINIUM.  369 

The  sulphide  is  so  unstable  that  it  decomposes  into  the 
hydroxide  and  hydrogen  sulphide  when  exposed  to  moist 
air.  When  a  soluble  hydroxide  is  added  to  a  solution  of 
a  salt  of  aluminium,  the  insoluble  hydroxide  is  precipitated ; 
but,  as  this  has  acid  properties,  it  is  dissolved  in  an  excess 
of  either  caustic  soda  or  caustic  potash.  Owing  to  the 
weak  basic  properties  of  the  hydroxide,  sodium  carbonate 
and  other  soluble  carbonates  precipitate,  not  the  carbonate, 
but  the  uncombined  hydroxide. 

EXPERIMENT  170.— Add  a  dilute  solution  of  sodium  carbonate 
to  a  dilute  solution  of  alum.  The  precipitate  is  the  hydroxide  : 

2AlK(SO4)a  +  3Na2C03  +  3H2O 

=  K2SO4  4-  3Na8SO4  +  3COa  +  2A1(OH),. 

Filter  off  and,  after  washing  carefully,  see  whether  the  precipi- 
tate is  the  carbonate.  Try  the  same  experiment  with  ammonium 
and  potassium  carbonates. 

When  an  aluminium  salt  in  solution  is  treated  with 
ammonium  sulphide,  the  hydroxide  is  precipitated.  Even 
if  the  sulphide  were  formed  it  would  be  decomposed  into 
the  hydroxide  and  hydrogen  sulphide  by  water. 

EXPERIMENT  171. — Add  ammonium  sulphide  to  a  solution  of 
alum.  The  precipitate  is  aluminium  hydroxide  : 

2A1K(SO4)3  +  3(NH4)2S  +  6H2O 

=  3(NH4)2S04  +  K2S04  +  3H2S  +  2A1(OH),. 

Rare  Elements  of  the  Aluminium  Group. — The  other 
members  of  the  aluminium  group  need  not  be  taken  up 
here.  The  existence  and  properties  of  two  of  them, 
gallium  and  scandium,  were  predicted  by  the  aid  of  the 
periodic  law,  as  has  been  pointed  out  (see  p.  227). 


CHAPTER   XXV. 
THE   LEAD    GROUP:    LEAD,   TIN,   AND   GERMANIUM. 

General. — The  only  two  members  of  this  group  that  need 
be  studied  here  are  lead  and  tin.  There  are  some  points 
of  resemblance  between  them,  but  there  are  also  marked 
differences. 

Lead,  Pb  (At.  Wt.  206.9). — Lead  occurs  in  combination 
in  several  forms  in  nature;  for  example,  as  the  sulphate, 
carbonate,  chromate,  and  sulphide.  The  sulphide,  PbS, 
known  as  galenite,  is  the  most  important  source  of  lead. 

Metallurgy. — The  extraction  of  the  metal  from  the  sul- 
phide is  accomplished  in  one  of  two  ways : 

(1)  By  heating  the  sulphide  with  iron,  when  the  latter 
combines  with  the  sulphur,  forming  iron  sulphide,  while 
the  lead  is  set  free. 

(2)  By  roasting  the  sulphide  until  it  is  partly  converted 
into  lead  oxide  and  lead  sulphate,  and  then  heating  the 
mixture  without  access  of  air,  when  the  following   two 
reactions  take  place: 

PbS  +  2PbO  =  3Pb  -1-  S02; 
PbS  +  PbS04  =  2Pb  +  2S02. 

The  lead  is  thus  set  free,  and  the  sulphur  is  driven  off 
as  sulphur  dioxide. 

Properties. — Lead  is  a  bluish-gray  metal  with  a  high 
lustre.  It  is  very  soft  and  not  very  strong.  It  melts  at 

370 


LEAD.  37* 

about  325°.  All  lead  compounds  are  poisonous.  Nitric 
acid  dissolves  it,  but  hydrochloric  and  dilute  sulphuric 
acids  do  not.  It  is  precipitated  in  metallic  form  from 
a  solution  of  one  of  its  salts  by  metallic  zinc.  The  forma- 
tion is  sometimes  called  the  "lead-tree"  or  "Arbor 
Saturni." 

EXPERIMENT  172. — Dissolve  5  grams  lead  nitrate  *  in  a  litre  of 
water  and  add  2-3  drops  dilute  nitric  acid.  Put  the  solution  in 
a  bottle.  By  means  of  a  thread  suspend  a  piece  of  clean  sheet 
zinc  in  the  solution,  and  let  it  stand.  The  lead  will  be  deposited 
slowly  in  crystalline  form.  At  the  same  time  the  zinc  will  pass 
into  solution.  The  zinc  simply  replaces  the  lead  : 

Zn  +  Pb(NOs)2  =  Zn(NO3)2  +  Pb. 

After  the  tree  is  formed,  filter  off  some  of  the  solution  and  see 
whether  zinc  is  contained  in  it  or  not.  There  will  probably  be 
some  lead  left,  so  that  in  order  to  detect  the  zinc  the  lead  will 
have  to  be  removed  first.  This  may  be  done  by  adding  sulphuric 
acid  and  alcohol.  The  sulphate  of  lead  is  thus  formed.  As  this 
is  somewhat  soluble  in  water  and  insoluble  in  alcohol,  the  latter 
is  added.  Filter  off  the  lead  sulphate,  and  to  the  filtrate  add 
just  enough  ammonia  to  neutralize  the  sulphuric  acid,  and  then 
ammonium  sulphide.  White  zinc  sulphide  is  precipitated. 

If  all  the  lead  is  not  precipitated  by  the  sulphuric  acid,  the 
precipitate  caused  by  ammonium  sulphide  will  not  be  white,  but 
more  or  less  inclined  towards  black,  according  to  the  quantity  of 
lead  sulphide  present.  All  the  lead  may  be  precipitated  in  the 
first  instance  by  first  adding  some  hydrochloric  acid  [What  effect 
will  this  have  on  the  solution  of  the  lead  salt  ?  Which  chlorides 
are  insoluble?]  and  then  passing  hydrogen  sulphide  through  the 
solution.  Filter  off  and  add  ammonia  and  ammonium  sulphide 
to  the  filtrate. 

Uses. — Lead  is  extensively  used  for  a  variety  of  purposes, 
as,  for  example,  for  sulphuric-acid  chambers,  for  evaporat- 
ing-pans  for  alum  and  sulphuric  acid,  for  shot,  for  water- 
pipes,  and  for  making  a  number  of  valuable  alloys.  The 

*  Instead  of  lead  nitrate,  the  acetate,  or  sugar  of  lead,  may  be  used. 


372  INTRODUCTION  TO  CHEMISTRY. 

use  of  lead  water-pipes  is  a  matter  of  much  importance 
from  a  sanitary  point  of  view.  Ordinary  drinking-water 
acts  only  very  slightly  upon  lead,  and  not  enough  is  dis- 
solved to  be  dangerous.  Nevertheless,  circumstances  may 
at  any  time  arise  that  will  increase  the  solvent  power  of 
the  water  and  serious  results  may  follow.  Air  and  water 
act  together  upon  lead  more  readily  than  when  the  air  is 
excluded.  In  moist  air  lead  tarnishes. 

Compounds  of  Lead  and  Oxygen.— Lead  forms  three  dis- 
tinct compounds  with  oxygen,  viz.:  lead  suboxide,  Pb20; 
lead  oxide,  PbO ;  and  lead  peroxide,  Pb02.  Red-lead,  or 
minium,  has  approximately  the  composition,  Pb304,  and 
is  perhaps  a  mixture  of  the  oxide  and  peroxide. 

Lead  oxide,  PbO,  is  known  by  the  name  of  litharge.  It. 
is  formed  by  the  oxidation  of  molten  lead  in  contact  with 
the  air.  When  litharge  is  heated  in  the  air  to  400°  it  takes 
up  oxygen  and  is  converted  into  minium,  or  red-lead, 
Pb304  (=  2PbO  +  Pb02).  When  heated  to  a  high  tem- 
perature this  gives  up  oxygen  and  is  again  converted  into 
yellow  lead  oxide.  Treated  with  nitric  acid,  a  part  is  dis- 
solved forming  lead  nitrate,  while  lead  peroxide,  a  brown 
powder,  remains  behind. 

EXPERIMENT  173. — Treat  a  little  minium  with  ordinary  dilute 
nitric  acid,  arid  note  the  change  in  color.  [Does  lead  pass  into 
solution  ?  How  do  you  know  ?] 

Lead  peroxide,  Pb02,  conducts  itself  somewhat  like 
manganese  dioxide.  When  treated  with  hydrochloric  acid 
chlorine  is  evolved : 

Pb02  -f  4HC1  =  PbCl2  +  2H20  +  C12. 

EXPERIMENT  174. — Treat  a  little  lead  peroxide  with  concentrated 
hydrochloric  acid  in  a  test-tube.  [In  what  form  is  the  lead  after 
the  experiment  ?  Is  the  product  soluble  or  insoluble  in  water?] 


COMPOUNDS  OF  LEAD.  373 

Heated  with  sulphuric  acid,  oxygen  is  given  off  and  lead 
sulphate  is  formed. 

EXPERIMENT  175. — Heat  some  lead  peroxide  with  concentrated 
sulphuric  acid.  [Is  oxygen  given  off?  What  is  left  behind  ?  Is 
it  soluble  or  insoluble  ?] 

Salts  of  Lead. — Among  the  more  important  salts  of  lead 
are  the  sulphate,  PbS04;  the  nitrate,  Pb(N03)2;  the  car- 
bonate, PbC03;  the  acetate,  Pb(02H302)2;  the  chromate, 
PbCrOj  and  the  sulphide,  PbS.  The  acetate  and  nitrate 
are  soluble  in  water;  the  others  are  not. 

Lead  acetate,  Pb(C2H302)2,  commonly  called  "sugar  of 
lead,"  is  the  lead  salt  of  acetic  acid,  C2H402,  which  is  the 
acid  contained  in  vinegar.  It  is  formed  by  dissolving 
litharge  in  acetic  acid. 

Insoluble  Salts  of  Lead. — The  sulphate,  chromate,  and 
chloride  have  already  been  referred  to.  They  are  formed 
by  adding  a  soluble  sulphate,  chromate,  and  chloride  to  a 
solution  of  a  lead  salt.  The  chromate  is  the  well-known 
chrome  yellow.  Lead  chloride  is  soluble  in  hot  water,  but 
only  slightly  soluble  in  cold  water.  It  crystallizes  from  its 
solution  in  hot  water. 

EXPERIMENT  176.— To  a  dilute  solution  of  lead  nitrate  or  acetate 
add  some  hydrochloric  acid.  Heat  and  thus  dissolve  the  precipi- 
tate, and  stand  it  aside.  On  cooling,  the  lead  chloride  will  crys- 
tallize out.  It  is  not  soluble  in  ammonia.  [Does  it  differ  from 
silver  chloride  in  this  respect?] 

Lead  carbonate,  PbC03,  occurs  in  nature  as  cerussite, 
and  is  precipitated  by  adding  lead  nitrate  to  a  solution  of 
ammonium  carbonate;  but  when  a  solution  of  a  lead  salt 
is  treated  with  a  normal  carbonate  of  sodium  or  potassium, 
a  basic  carbonate  is  precipitated.  When,  for  example,  an 
excess  of  sodium  carbonate  is  added  to  a  solution  of  lead 
nitrate,  the  precipitate  has  the  composition  3Pb0.2C02  -j- 


374  INTRODUCTION   TO   CHEMISTRY. 

H30.  The  salts  usually  obtained  are  more  complicated 
than  this.  Basic  lead  carbonate  is  prepared  and  used  ex- 
tensively under  the  name  of  white-had,  as  a  pigment.  An 
objection  to  white-lead  paint  is  that  it  turns  dark  when 
exposed  to  hydrogen  sulphide.  It  also  turns  yellow  in 
consequence  of  the  action  of  some  substance  contained  in 
the  oil  with  which  the  lead  carbonate  is  mixed. 

Lead  sulphide,  PbS,  is  the  important  mineral  galenite 
to  which  reference  has  been  made.  The  compound  is 
precipitated  by  passing  hydrogen  sulphide  through  a  solu- 
tion of  a  lead  salt,  or  by  adding  a  soluble  sulphide  to  such 
a  solution. 

[How  can  you  distinguish  between  a  lead  and  a  barium 
salt  without  using  hydrogen  sulphide?  Between  lead  and 
silver  without  using  hydrogen  sulphide  or  hydrochloric 
acid  ?  By  hydrochloric  acid  alone  ?] 

Tin,  Sn  (At.  Wt.  118.5). — -Tin  occurs  in  nature  mostly 
as  tin-stone,  or  cassiterite,  which  is  the  oxide  Sn02. 

Metallurgy. — The  ores  are  roasted  for  the  purpose  of 
getting  rid  of  the  sulphur  and  arsenic,  and  the  oxide  is 
then  heated  with  coal  in  a  furnace.  After  the  reduction 
is  complete  the  tin  is  drawn  off  and  cast  in  bars.  This  tin 
is  impure,  and  when  again  slowly  melted,  that  which  first 
melts  is  purer.  By  letting  it  run  off  as  soon  as  it  melts, 
the  comparatively  difficultly  fusible  alloy  remains  behind. 
The  commercial  variety  known  as  Banco,  tin  is  the  purest. 
This  is  made  at  Banca  in  the  East  Indies.  Block-tin,  made 
in  England,  is  also  comparatively  pure. 

Properties. — It  is  a  white  metal,  which  in  general  ap- 
pearance resembles  silver.  It  is  soft  and  malleable,  and 
can  be  hammered  out  into  very  thin  sheets,  forming  thus 
the  well-known  tin-foil.  At  200°  it  is  brittle.  It  melts 


TIN.  375 

at  228°.  It  remains  unchanged  in  the  air  at  ordinary 
temperatures.  It  dissolves  in  hydrochloric  acid,  forming 
stannous  chloride,  SnCl2;  in  sulphuric  acid,  forming 
stannous  sulphate,  SnS04,  sulphur  dioxide  being  evolved 
at  the  same  time.  [Explain  this.]  Ordinary  concentrated 
nitric  acid  oxidizes  it,  the  product  being  a  compound  of 
tin,  oxygen,  and  hydrogen,  known  as  metastannic  acid, 
which  is  a  white  powder  insoluble  in  nitric  acid  and  in 
water. 

Uses. — It  is  used  in  making  alloys,  of  which  bronze,  soft 
solder,  and  britannia  metal  are  the  most  important.  It  is 
used  most  extensively  for  protecting  other  metals,  as  in  the 
tinware  vessels  in  such  common  use,  which  are  made  of 
sheet-iron  covered  with  a  layer  of  tin. 

Alloys. — Bronze  has  already  been  referred  to  under 
Copper.  Soft  solder  is  made  of  equal  parts  of  tin  and 
lead,  or  of  two  parts  of  tin  and  one  of  lead.  Britannia 
metal  is  composed  of  nine  parts  of  tin  and  one  of  antimony. 
Tin  amalgam  is  made  by  bringing  tin  and  mercury 
together,  and  is  used  in  the  silvering  of  mirrors. 

Stannous  and  Stannic  Compounds.  —  Tin  forms  two 
classes  of  compounds,  the  xtannous  and  stannic  compounds. 
These  do  not  bear  to  each  other  the  same  relation  that 
cuprous  and  cupric  compounds  do.  [What  is  this  ?]  In 
stannous  compounds  the  tin  appears  to  be  bivalent,  as  in- 
dicated by  the  formulas  SnCl2,  SnO,  SnS,  which  respec- 
tively represent  stannous  chloride,  oxide,  and  sulphide. 
In  stannic  compounds,  on  the  other  hand,  the  tin  appears 
to  be  quadrivalent,  as  indicated  by  the  formulas  SnCl^, 
Sn02,  and  SnS2,  which  respectively  represent  stannic 
chloride,  oxide,  and  sulphide. 

In  general,  stannous  compounds  are  readily  converted 
into  stannic  compounds. 


376  INTRODUCTION    TO   CHEMISTRY. 

Stannous  chloride,  SnCl2,  is  formed  by  dissolving  tin 
in  hydrochloric  acid.  If  a  solution  of  stannous  chloride 
is  added  to  a  solution  of  mercuric  chloride,  or  corrosive 
sublimate,  the  latter  is  reduced  to  rnercurous  chloride,  and 
this,  being  insoluble  in  water,  appears  as  a  precipitate. 
When  stannous  chloride  and  mercuric  chloride  are  heated 
together  in  solution,  metallic  mercury  is  formed  : 


2IIgCl,  +  SnCl,  =  SHgCl  +  SnCl4; 
HgCl,  +  SnCl2  =  Hg  +  SnCl4. 

EXPERIMENT  177.  —  Dissolve  a  few  grams  of  tin  in  warm  diluted 
hydrochloric  acid.  Add  a  little  of  this  solution  to  a  solution  of 
mercuric  chloride.  A  white  precipitate  of  mercurous  chloride 
will  be  formed.  Heat  the  two  solutions  together,  and  notice  the 
formation  of  metallic  mercury,  which  appears  as  a  gray  powder. 

Stannic  oxide,  Sn02  ,  occurs  in  nature  as  tin-stone.  It 
is  obtained  by  burning  tin  in  the  air.  When  melted 
together  with  caustic  soda  it  dissolves  as  sodium  stannate. 
This  action  suggests  that  which  takes  place  when  silicon 
dioxide  is  melted  with  an  alkali  and  a  silicate  is  formed, 
and  when  carbon  dioxide  arid  an  alkali  are  brought 
together.  The  formulas  of  the  products  in  these  cases  are 
similar,  viz.,  Na2Sn03,  Na2Si03,  and  Na2COs. 

Stannic  Hydroxide,  Sn(OH)4,  and  Stannic  Acid,  HeSn03. 
—  Stannic  hydroxide,  Sn(OH)4,  is  perhaps  formed  when 
a  solution  of  stannic  chloride  in  water  is  boiled.  The  pre- 
cipitate obtained  has,  however,  the  composition  H2Sn03, 
and  this  is  known  as  stannic  acid.  Stannic  acid  is  precipi- 
tated also  by  treating  a  solution  of  a  stannate  with  just 
enough  of  an  acid  to  effect  decomposition.  The  decom- 
position with  hydrochloric  acid  takes  place  as  represented 
in  the  equation 

2HC1  =  2NaCl  +  HaSn08, 


STANNIC   COMPOUNDS.  377 

Metastannic  Acid. — When  tin  is  treated  with  concen- 
trated nitric  acid  it  is  converted  into  a  white  powder  which 
is  insoluble  in  water  and  in  acids.  Stannic  acid  is  insolu- 
ble in  water,  but  is  easily  soluble  in  hydrochloric,  nitric, 
and  sulphuric  acids.  The  two  acids  cannot,  therefore,  be 
identical  though  they  appear  to  have  the  same  composition. 
The  product  formed  by  oxidizing  tin  with  nitric  acid  is 
called  metastannic  acid. 

Stannic  chloride,  SnCl4,  is  made  by  heating  tin  in 
chlorine.  It  is  a  heavy  liquid,  that  distils  at  120°  without 
decomposition.  It  fumes  in  the  air  very  strongly.  It  has 
a  marked  affinity  for  water,  and  is  used  as  a  dehydrating 
agent  in  a  number  of  reactions.  It  has  long  been  known 
by  the  name  spiritus  fumans  Libavii.  In  solution  it  is 
obtained  by  dissolving  tin  in  aqua  regia.  In  this  case  the 
stannous  chloride  formed  by  the  action  of  the  hydrochloric 
acid  on  the  tin  is  oxidized  by  the  nitric  acid: 

SnCl2  +  2HC1  +  0  =  SnCl4  -f  H20. 

Stannic  sulphide,  SnS2 ,  is  a  yellow  substance  resembling 
arsenic  sulphide.  It  is  formed  by  passing  hydrogen  sul- 
phide through  a  dilute  solution  of  stannic  chloride.  It  is 
soluble  in  ammonium  sulphide. 

EXPERIMENT  178. — Dissolve  a  little  tin  in  aqua  regia.  Dilute 
the  solution,  heat  it,  and  pass  hydrogen  sulphide  through  it. 
Filter  off,  wash,  and  treat  with  ammonium  sulphide.  [Does  the 
precipitate  dissolve  ?  Add  an  acid  to  the  solution.  What  takes 
place  ?] 

How  to  Distinguish  Tin  from  Other  Metals. — A  pecu- 
liarity of  tin  which  distinguishes  it  from  most  other  metals 
is  its  conduct  towards  nitric  acid.  As  already  stated, 
instead  of  dissolving  in  the  acid,  it  is  converted  into  a 
white,  insoluble  compound — metastannic  acid.  Antimony 
is  also  converted  into  a  white  oxide  by  nitric  acid,  but 


37**  INTRODUCTION   TO  'CHEMISTRY. 

antimony  does  not  dissolve  in  hydrochloric  acid,  while  tin 
does. 

EXPERIMENT  179. — Treat  a  little  tin  with  strong  nitric  acid,  and 
notice  the  formation  of  the  white  metastannic  acid.  [Is  it  soluble 
in  water  ?]  Treat  a  little  antimony  in  the  same  way.  Now  treat 
each  element  separately  with  hydrochloric  acid. 

EXPERIMENT  180. — Examine  a  small  piece  of  solder,  and  see 
whether  it  contains  lead  and  tin. — Treat  with  aqua  regia;  dilute 
with  water.  [Will  all  the  lead  pass  into  solution  under  these  circum- 
stances ?J  Heat  and  pass  hydrogen  sulphide  through  the  much-di- 
luted solution.  Filter  off  the  precipitate  ;  wash  with  hot  water  ; 
treat  with  yellow  ammonium  sulphide  ;  filter  ;  add  an  acid  to  the 
filtrate.  [Explain  what  takes  place  in  each  step.]  The  formation  of  a 
yellow  precipitate,  which  is  soluble  in  ammonium  sulphide,  is  not 
conclusive  evidence  that  tin  is  present,  for  arsenic  sulphide  has 
similar  properties.  In  order  to  distinguish  between  them  advan- 
tage may  be  taken  of  the  fact  that  arsenic  sulphide  is  soluble  in  a 
solution  of  ammonium  carbonate,  while  stannic  sulphide  is  not. 
Treat  some  of  the  precipitate  with  a  solution  of  ammonium  car- 
bonate ;  filter ;  add  an  acid,  when,  if  any  arsenic  sulphide  is  in 
solution,  it  will  be  precipitated. 

EXPERIMENT  181. — Examine  a  small  piece  of  bronze,  and  show 
that  it  consists  of  tin  and  copper.  After  getting  the  two  metals 
in  solution  by  means  of  aqua  regia,  dilute,  heat,  and  pass  hydro- 
gen sulphide  through  until  the  solution  is  saturated.  Filter  ; 
wash  ;  treat  with  yellow  ammonium  sulphide.  Filter  ;  acidify  ; 
show  that  the  yellow  precipitate  is  not  arsenic  sulphide.  Dissolve 
the  black  precipitate,  which  is  for  the  most  part  insoluble  in  am- 
monium sulphide,  in  nitric  acid.  [What  change  will  the  copper 
sulphide  undergo  when  treated  with  nitric  acid  ?]  Treat  a  little 
of  the  solution  with  caustic  soda,  and  boil.  [What  changes  take 
place  ?]  Filter  and  wash.  Mix  some  of  the  black  precipitate  with 
sodium  carbonate,  and  heat  in  the  reducing  flame  of  the  blow- 
pipe. [What  evidence  of  the  presence  of  copper  do  you  thus 
get?] 


Qwv 


CHAPTER   XXVI. 
THE   IRON   GROUP:    IRON,   COBALT,    NICKEL. 

Iron,  Fe  (At.  "Wt.  56). — At  the  present  time  it  is  un- 
doubtedly true  that  iron  is  the  most  important  metal  for 
man.  It  is  not  improbable,  however,  that  in  the  future 
aluminium  may  take  its  place  for  many  purposes,  though 
there  appears  to  be  no  immediate  prospect  of  this  inter- 
ference with  the  iron  industry. 

Occurrence. — Iron  occurs  in  the  form  of  the  oxides, 
Fe^  and  Fe203;  as  the  carbonate,  FeC03;  in  combina- 
tion with  sulphur  as  iron  pyrites,  pyrite,  FeS2;  and  as 
silicates  and  hydrated  oxides,  or  hydroxides.  The  com- 
pounds principally  used  in  making  iron  are  magnetite, 
Fe304;  haematite,  Fe203;  brown  iron  ore,  Fe403(OH)6; 
and  spathic  iron,  or  siderite,  FeC03. 

Metallurgy. — After  the  ores  are  broken  up,  they  are  first 
roasted,  in  order  to  drive  off  water  from  the  hydroxides; 
to  decompose  carbonates ;  to  oxidize  sulphides ;  and,  as  far 
as  possible,  to  convert  the  oxides  into  ferric  oxide,  Fe203 , 
which  is  the  most  easily  reducible  of  the  oxides  of  iron. 
After  the  ores  are  prepared  in  this  way  they  are  reduced 
by  heating  them  with  carbon  and  fluxes  in  the  blast-fur- 
nace, when  the  iron  collects  in  the  molten  condition  under 
the  so-called  slag  at  the  bottom  of  the  furnace.  Blast- 
furnaces differ  somewhat  in  construction,  but  the  essential 
parts  are  represented  in  Fig.  56. 

379 


38o  INTRODUCTION    TO   CHEMISTRY. 

The  inner  cavity  of  the  furnace  is  narrow  at  the  top  and 
bottom,  as  is  shown  in  the  figure.  Through  pipes,  known 
as  tuyeres,  such  as  that  represented 
at  the  lower  part  of  the  left-hand 
side  of  the  figure,  hot  air  is  blown 
into  the  furnace  to  facilitate  the 
combustion.  In  modern  furnaces 
arrangements  are  made  above  for 
carrying  off  the  gases  and  utilizing 
them  as  fuel.  The  inner  walls  are 
built  of  fire-bricks,  and  these  are 
surrounded  by  ordinary  bricks,  or 
stone-work.  The  furnaces  vary 
in  height  from  25  to  80  or  90  feet, 
an  average  height  being  about  45 
feet.  The  reduction  of  the  ores 
is  accomplished  by  placing  in  the 
furnace  alternating  layers  of  coke 
or  charcoal,  and  the  ores  mixed 
with  proper  fluxes.  The  nature 
°^  the  flux  depends  upon  the  ore. 
If  this  contains  silicon  dioxide  or  clay,  lime  is  added; 
while,  if  it  contains  considerable  lime,  minerals  rich  in 
silicic  acid  are  used,  such  as  feldspar,  clay -slate,  etc.  The 
object  of  the  flux  is  to  form  a  slag  in  which  the  reduced 
iron  collects,  and  by  which  it  is  protected  from  oxidation. 
When  the  fire  is  once  started  in  a  blast-furnace  the  opera- 
tion of  reduction  is  continuous  until  the  furnace  is  burned 
out.  Alternate  layers  of  ore  and  flux  and  carbon  are 
added,  and,  as  the  reduced  iron  collects  below,  it  is  from 
time  to  time  drawn  off  and  allowed  to  solidify  in  moulds 
of  sand.  The  operation  requires  close  attention.  The 
ores  must  be  carefully  studied,  and  the  nature  and  amount 
of  flux  regulated  according  to  the  character  of  the  ore,  as 
above  stated.  Then,  too,  the  temperature  of  the  furnace 


VARIETIES  OF  IRON.  3Sl 

is  a  matter  of  importance,  and  must  be  watched,  and 
regulated  by  means  of  the  blast.  The  reduction  is  largely 
accomplished  by  carbon  monoxide.  In  the  lower  part  of 
the  furnace  the  fuel  burns  to  carbon  dioxide,  but  this 
comes  in  contact  with  hot  carbon,  and  is  then  reduced  to 
the  monoxide.  The  hot  monoxide  in  contact  with  the 
oxides  of  iron  reduces  these,  and  is  itself  converted  into 
the  dioxide.  A  large  proportion  of  the  carbon  monoxide, 
however,  escapes  oxidation,  and  this  is  carried  off  from  the 
top  to  the  bottom  of  the  furnace  by  properly-arranged 
pipes,  and  is  then  utilized  as  fuel.  A  furnace  lasts  from 
two  to  twenty  years,  and  sometimes  longer. 

Varieties  of  Iron. — The  iron  obtained  as  above  described 
is  known  as  pig-iron  or  cast-iron.  It  is  very  impure,  con- 
taining carbon,  phosphorus,  sulphur,  silicon,  etc.  If, 
when  drawn  from  the  furnace,  the  iron  is  cooled  rapidly, 
nearly  all  the  carbon  contained  in  it  remains  in  chemical 
combination,  and  the  iron  has  a  silver-white  color.  This 
product  is  known  as  white  cast-iron.  If  the  iron  cools 
slowly,  most  of  the  carbon  separates  as  graphite,  and  this 
being  distributed  through  the  mass  gives  it  a  gray  color. 
This  product  is  known  as  gray  cast-iron.  If  the  ore  con- 
tains considerable  manganese,  this  is  reduced  with  the  iron, 
and  iron  made  from  such  ores  and  containing  manganese 
has  the  power  to  take  up  more  carbon  than  ordinary  iron. 
This  product,  containing  from  3.5  to  6  per  cent  combined 
carbon,  is  known  as  spie gel-iron. 

All  varieties  of  cast-iron  are  brittle,  and  easily  fusible. 
The  gray  iron  fuses  at  a  lower  temperature  than  the  white, 
and  is  not  as  brittle ;  it  is  therefore  well  adapted  to  making 
castings.  When  cast-iron  is  treated  with  hydrochloric  acid 
the  carbon  which  is  present  in  combined  form  is  given  off 
in  combination  with  hydrogen  as  hydrocarbons,  some  of 
which  have  a  disagreeable  odor.  This  is,  of  course,  the 


382  INTRODUCTION   TO  CHEMISTRY. 

cause  of  the  bad  odor  noticed  on  dissolving  ordinary  cast- 
iron  in  acids.  The  uncombined  or  graphitic  carbon,  on 
the  other  hand,  remains  undissolved.  Owing  to  its  brittle- 
ness,  cast-iron  cannot  be  welded.  When  the  carbon, 
silicon,  and  phosphorus  are  removed  the  iron  becomes 
tough  and  malleable,  and  its  melting-point  is  much  raised. 
The  product  thus  obtained  is  known  as  wrought -iron. 

Puddling. — The  puddling-furnace  has  a  fiat,  oval  hearth 
and  a  low,  arched  roof.  The  sides  of  the  hearth  are  lined 
with  iron  ore  (oxide).  Coal  is  burned  on  a  grate,  and  the 
flame  passes  into  the  furnace  at  one  end  and  out  at  the 
other,  thus  coming  in  contact  with  the  roof  and  the  charge 
of  iron.  The  cast-iron  is  melted,  and  the  carbon  and 
silicon  are  removed  from  it,  partly  by  the  oxygen  of  the 
air,  but  principally  by  that  in  the  iron  ore,  which  is  itself 
thus  reduced  to  wrought-iron. 

Wrought-iron  contains  less  than  0.  G  per  cent  of  carbon, 
and,  as  the  percentage  of  carbon  decreases,  the  malleability 
increases  and  the  melting-point  rises.  The  melting-point 
of  good  wrought-iron  is  from  1900°  to  2100°.  Small 
quantities  of  sulphur,  phosphorus,  silicon,  and  manganese 
exert  a  very  marked  influence  upon  its  properties.  The 
process  of  welding  consists  in  heating  two  pieces  of  iron  to 
a  high  temperature,  putting  some  borax  upon  one  of  them, 
laying  them  together,  and  hammering,  when,  as  is  well 
known,  they  adhere  firmly  together.  The  object  of  the 
borax  is  to  keep  the  surfaces  bright,  which  it  does  by  unit- 
ing with  the  oxide  and  forming  an  easily  fusible  borate. 

Bessemer  Process. — Molten  cast-iron  is  poured  into  a 
large  vessel  called  a  converter,  Fig.  57.  The  carbon  and 
silicon  are  entirely  oxidized,  and  removed  by  a  blast  of  air 
forced  through  the  metal  from  below.  No  fuel  is  used,  as 
the  heat  generated  by  the  oxidation  of  the  carbon  and 


VARIETIES  OF  IRON. 


383 


silicon  is  sufficient  to  raise  the  temperature  above  2100°. 
By  adding  molten  cast-iron  to  the  product,  steel  of  the 
desired  percentage  of  carbon  is  obtained. 

The  Bessemer  process  is  now  employed  on  an  enormous 
scale,  there  being  a  large  demand  for  the 
product.  It  is  used  in  making  cannon, 
rails,  axles,  etc.  Iron  containing  more 
than  a  very  small  percentage  of  phos- 
phorus is  not  adapted  to  the  manufacture 
of  Bessemer  steel  in  the  ordinary  way; 
but  it  has  been  found  that,  if  the  con- 
verters are  lined  with  lime-stone,  such 
iron  may  be  used.  Under  these  circum- 
stances the  phosphorus  is  oxidized,  and 
with  the  lime-stone  forms  calcium  phos- 
phate, which  is  of  value  as  a  fertilizer 
(see  Calcium  Phosphate).  This  process  FIG.  57. 

is  known  as  the  Thomas- Gilchrist  or  the  basic-lining 
process. 

Siemens-Martin  Furnace. — This  is  simply  a  reversible 
puddling-furnace  in  which  gas  is  used  as  fuel.  The  process 
based  upon  the  use  of  this  furnace  is  chemically  the  same 
as  that  of  the  puddling-furnace. 

Steel  and  Wrought-iron. — The  product  of  the  puddling- 
furnace  is  called  wrought-iron,  while  that  obtained  by  the 
Bessemer  process  and  that  from  the  Siemens-Martin  fur- 
nace are  called  steel.  Bessemer  steel  often  contains  less 
than  0.6  per  cent  of  carbon;  and  Siemens-Martin  steel  is 
in  fact  the  finest  wrought-iron. 

Uses. — Any  statement  in  regard  to  the  applications  of 
the  three  varieties  of  iron,  viz.,  cast-iron,  steel,  and 
wrought-iron,  would  be  superfluous. 


384  INTRODUCTION    TO   CHEMISTRY. 

Properties  of  Iron. — Pure  iron  is  almost  unknown.  Of 
the  commercial  varieties,  it  follows  from  what  has  been 
said  that  wrought-iron  is  the  purest.  That  which  is  used 
for  piano-strings  is  the  purest  commercial  iron ;  it  contains 
only  about  0. 3  per  cent  of  impurities.  Pure  iron  can  be 
made  in  the  laboratory  by  igniting  the  oxide  or  oxalate  in 
a  current  of  hydrogen,  and  by  reducing  ferrous  chloride 
in  hydrogen.  In  larger  quantity  it  can  be  prepared  by 
melting  the  purest  wrought-iron  in  a  lime  crucible  by 
means  of  the  oxhydrogen  flame.  The  impurities  are  taken 
up  by  the  crucible,  and  a  regulus  of  the  pure  metal  is  left 
behind.  That  made  by  reduction  of  the  oxide  or  oxalate 
is,  of  course,  in  finely-divided  condition.  If  in  its  prep- 
aration the  temperature  is  kept  as  low  as  possible,  the 
product  takes  fire  when  brought  in  contact  with  the  air; 
while  if  the  temperature  is  high,  the  product  has  not  this 
power.  Pure  iron  is  white  and  is  one  of  the  hardest 
metals.  Its  melting-point  is  higher  than  that  of  wrought- 
iron.  Pure  iron  is  attracted  by  the  magnet.  In  contact 
with  a  magnet,  or  when  placed  in  a  coil  through  which  an 
electric  current  is  passing,  it  becomes  a  magnet;  but  the 
purer  it  is  the  sooner  it  loses  the  magnetic  power  when 
removed  from  the  magnet  or  the  coil.  Steel,  however, 
retains  its  magnetism.  When  heated  to  a  sufficiently  high 
temperature  iron  burns,  and  forms  the  oxide,  Fe304.  This 
takes  place  much  more  easily  in  oxygen  than  in  the  air. 
In  dry  air  iron  does  not  undergo  change,  but  in  moist  air 
it  rusts,  or  it  becomes  covered  with  a  layer  of  oxide  and 
hydroxide,  which  is  formed  by  the  action  of  the  air,  carbon 
dioxide,  and  water.  The  presence  of  salts  in  solution 
facilitates  the  rusting.  Various  methods  are  adopted  to 
protect  iron  from  this  change,  most  of  which  are,  however, 
purely  mechanical.  A  method  that  promises  valuable 
results  is  that  invented  by  Barff.  This  consists  in  intro- 
ducing the  iron  into  water-vapor  at  a  temperature  of  650°, 


COMPOUNDS   OF  IRON.  385 

when  it  becomes  covered  with  a  firmly-adhering  layer  of 
oxide. 

Iron  dissolves  in  acids  with  evolution  of  hydrogen,  and 
generally  with  formation  of  ferrous  salts : 


Fe  +  H2S04  =  FeS04  +  H2. 

When  cold  nitric  acid  is  used,  ferrous  nitrate  and  am- 
monium nitrate  are  the  products;  if  the  acid  is  warmed, 
ferric  nitrate  and  oxides  of  nitrogen  are  formed.  When 
an  iron  wire  which  has  been  carefully  polished  is  intro- 
duced for  an  instant  into  red  fuming  nitric  acid  it  can 
afterward  be  put  into  ordinary  nitric  acid  without  under- 
going change.  It  is  said  to  be  in  the  passive  state;  and 
the  commonly-accepted  explanation  of  the  phenomenon  is 
that  the  wire  is  covered  with  a  thin  layer  of  oxide.  As, 
however,  the  passive  condition  is  lost  by  contact  with  an 
ordinary  wire,  the  explanation  does  not  appear  to  be 
adequate. 

Iron  forms  Two  Series  of  Compounds. — Iron,  like  mer- 
cury, copper,  and  tin,  forms  two  series  of  compounds  that 
differ  markedly  from  each  other.  These  are  the  ferrous 
and/erric  compounds.  Thus  with  chlorine  it  forms  two 
chlorides,  one  of  which,  ferrous  chloride,  has  the  composi- 
tion expressed  by  the  formula  FeCl2;  the  other,  ferric 
chloride,  by  FeCl3.  It  appears  from  a  study  of  the  specific 
gravities  of  the  vapors  of  these  chlorides  that  the  above 
formulas  should  be  doubled,  so  that  ferrous  chloride  is 
now  commonly  represented  by  Fe2Cl4 ,  and  ferric  chloride 
by  Fe,Cl.. 

Similarly  there  are  two  oxides,  FeO  and  Fe203;  two 
sulphates,  ferrous  sulphate,  FeS04,  and  ferric  sulphate, 
Fe2(S04)3,  etc. 


386  INTRODUCTION   TO   CHEMISTRY. 

Ferrous  Compounds  are  converted  into  Ferric  Compounds 
by  Oxidation. — Ferrous  compounds  show  a  tendency  to 
pass  into  ferric  compounds  by  simple  contact  with  the  air; 
and  are  readily  converted  into  these  by  oxidizing  agents, 
such  as  nitric  acid,  potassium  chlorate,  etc.  When,  for 
example,  ferrous  hydroxide,  Fe(OIi).,  ,*  is  exposed  to  the 
air  suspended  in  water,  it  changes  to  ferric  hydroxide, 
Fe(OH)3.  The  change  is  represented  by  the  equation 

2Fe(OH)2  +  H20  -f  0  =  2Fe(OH)3. 

So,  also,  when  ferrous  chloride  is  left  standing  in  hydro- 
chloric-acid solution  it  changes  to  ferric  chloride,  and  the 
change  is  rapidly  effected  by  boiling  with  a  little  nitric 
acid: 

2FeCl,  +  2HC1  +  0  =  2FeCls  +  H20. 

Ferrous  chloride,  FeCl2 ,  is  formed  by  dissolving  iron  in 
hydrochloric  acid. 

EXPERIMENT  182.— Dissolve  a  little  iron  wire  in  dilute  hydro- 
chloric acid.  Hydrogen  is  evolved,  accompanied  by  small  quan- 
tities of  other  gases,  the  formation  of  which  is  due  to  the  presence 
of  impurities  in  the  iron,  and  carbon  is  left  undissolved  as  a  black 
i'esidue.  To  a  little  of  the  solution  in  a  test-tube  add  at  once 
caustic  soda.  This  precipitates  ferrous  hydroxide,  Fe(OH)3, 
which  changes  color  rapidly.  Pure  ferrous  hydroxide  is  white. 
As  it  passes  to  the  ferric  condition  it  becomes  dirty  green,  and 
darker  and  darker  until  it  is  reddish  brown.  Heat  another  por- 
tion of  the  solution  of  ferrous  chloride  to  boiling,  add  two  or 
three  drops  of  concentrated  nitric  acid,  and  boil  again.  Repeat 
this  operation  two  or  three  times.  The  ferrous  chloride  is  thus 
oxidized  to  ferric  chloride.  It  will  be  noticed  that  the  color  of 

*  If  ferrous  chloride  has  the  formula  Fe2Cl4 ,  it  seems  probable 
that  the  formula  of  ferrous  hydroxide  is  Fe2(OH)4.  We  have  no  di- 
rect evidence  bearing  upon  this,  and  hence  the  simpler  formula  may 
be  used  here,  particularly  as  we  are  for  the  present  interested  mainly 
in  the  composition  of  the  compound. 


FERROUS  AND  FERRIC  COMPOUNDS.  387 

the  solution  after  the  oxidation  is  reddish  yellow,  whereas  before 
the  oxidation  it  was  nearly  colorless  or  greenish.  Add  caustic 
soda  to  the  solution  of  ferric  chloride.  A  reddish  brown  precipi- 
tate of  ferric  hydroxide  will  be  formed.  Just  as  in  this  case  we 
have  passed  from  ferrous  chloride  to  ferric  chloride  by  oxidation, 
so  we  can  pass  back  again  to  the  ferrous  compound.  Thus,  by 
adding  a  little  zinc  to  a  solution  of  ferric  chloride  in  which  hy- 
drochloric acid  is  present,  the  hydrogen  evolved  extracts  chlorine 
from  the  ferric  chloride  and  converts  it  into  ferrous  chloride  : 

FeCl3  +  H  =  FeCla  +  HC1. 

Ferrous  Sulphate,  FeS04  -f  7H20.—  This  salt,  which  is 
commonly  known  as  " green  vitriol"  or  "copperas,"  is 
formed  by  the  action  of  sulphuric  acid  on  iron.  [What  is 
"  white  vitriol,"  "blue  vitriol"?]  It  undergoes  change 
in  the  air,  being  converted  into  a  compound  containing 
ferric  sulphate,  Fe2(S04)3,  and  ferric  hydroxide: 

6FeS04  +  30  +  3H20  =  2Fe2(S04)3  -f  2Fe(OH)3. 

Iron  alum,  FeK(S04),  -j-  12H20,  is  formed  by  bringing 
ferric  sulphate  and  potassium  sulphate  together.  It 
resembles  ordinary  alum,  A1K(S04)2  -J-  12H20,  but  differs 
from  it  in  containing  iron  instead  of  aluminium. 

Ferrous  oxide,  FeO,  cannot  be  prepared  in  pure  condi- 
tioii  on  account  of  its  great  affinity  for  oxygen. 

Ferric  oxide,  Fe203 ,  occurs  in  nature  in  lustrous  crystals 
as  hematite,  and  in  other  valuable  ores  of  iron.  The 
hydroxide  corresponding  to  this — viz.,  ferric  hydroxide, 
Fe(OH)3 — is  analogous  in  composition  and  properties  to 
aluminium  hydroxide.  It  is  a  weak  base,  but,  unlike 
aluminium  hydroxide,  it  does  not  form  compounds  with 
bases.  Hence  it  does  not  dissolve  in  caustic  soda  and 
caustic  potash.  [Try  it.  Suppose  a  solution  contains  an 
aluminium  salt  and  a  ferric  salt,  and  caustic  soda  is  added, 


388  INTRODUCTION   TO  CHEMISTRY. 

what  will  first  take  place  ?  If  more  is  added  and  the  solu- 
tion filtered,  where  will  the  aluminium  be  found,  and 
where  the  iron  ?] 

Certain  natural  compounds  of  iron  appear  to  be  deriva- 
tives of  the  hydroxide  FeO.OH,  which  corresponds  to  the 
aluminium  compound  A10.0H,  and  to  metaboric  acid, 
BO.  OH.  Thus  magnetite  is  believed  to  be  the  ferrous  salt 

of  this  acid  as  represented  by  the  formula 


and  franklinite  is  probably  the  corresponding  zinc  salt 

FeO.O     -„ 

FeO.O>Zl1' 

Ferroso-ferric  oxide,  Fe30t,  or  magnetic  oxide  of  iron, 
is  found  in  nature  in  the  form  of  loadstone.  It  is  formed 
when  iron  is  burned  in  oxygen  (see  Experiment  24). 

Ferric  Acid,  H2Fe04.  —  It  is  interesting  to  note  that  iron 
combines  with  a  larger  proportion  of  oxygen  than  is  con- 
tained in  any  of  the  compounds  thus  far  mentioned,  and 
then  forms  an  acid.  Potassium  ferrate  has  the  composi- 
tion represented  by  the  formula  K2Fe04. 

Sulphides  of  Iron.  —  The  sulphides  of  iron  have  been 
repeatedly  mentioned.  Ferrous  sulphide,  FeS,  is  made  by 
heating  sulphur  and  iron  together  in  proper  proportion?. 
It  is  used  in  making  hydrogen  sulphide  [Explain  how]. 

Iron  pyrites,  or  pyrite,  FeS2,  is  a  yellow  crystallized 
substance  found  very  abundant  in  nature.  When  heated 
in  a  closed  tube,  sulphur  is  given  off.  When  heated  in  an 
open  vessel,  as  upon  a  shallow  iron  pan,  the  sulphur  is 
oxidized  to  sulphur  dioxide,  and  the  iron  is  left  in  the 
form  of  the  oxide.  [Verify  these  statements  by  experi- 
ment.] 


NICKEL—  COBAL  T.  389 

Nickel,  Ni  (At.  Wt.  58.7),  is  found  in  meteoric  iron 
and  in  combination  with  arsenic.  It  forms  two  series  of 
salts  corresponding  to  the  two  hydroxides  nickelous  hy- 
droxide, Ni(OH)2,  and  nickelic  hydroxide,  M(OH)3. 

Most  nickel  salts  are  colored  green. 

Alloys  of  nickel  are  extensively  used.  Argentan  or 
German  silver  consists  of  copper,  zinc,  and  nickel. 
Various  nickel  alloys  are  used  for  making  coins.  The 
5-  and  3-cent  pieces  of  the  United  States  are  made  of  an 
alloy  consisting  of  25  per  cent  nickel  and  75  per  cent 
copper. 

Nickel  is,  further,  extensively  used  in  nickel-plating. 
Iron  is  covered  with  a  thin  layer  of  the  metal  to  protect  it 
from  rusting. 

Cobalt,  Co  (At.  Wt,  59),  is  found  in  combination  with 
arsenic  and  sulphur,  and  also  in  small  quantities  accom- 
panying nickel  in  meteoric  iron. 

The  salts  of  cobalt  are  red  in  combination  with  water, 
and  blue  when  dried.  If  marks  are  made  on  paper  with 
a  dilute  solution  of  one  of  the  salts  the  color  is  not  per- 
ceptible. If,  however,  the  paper  is  held  before  a  fire,  the 
salt  loses  water  and  turns  blue,  and,  as  the  blue  is  more 
intense  than  the  red,  it  is  visible.  When  the  salt  is  again 
moistened  it  becomes  invisible.  This  is  the  basis  of  the 
preparation  of  the  so-called  sympathetic  inks. 


CHAPTER   XXVII. 
MANGANESE.— CHROMIUM.— URANIUM. 

Manganese,  Mn  (At.  Wt.  55). — Manganese  is  found  in 
nature  in  the  form  of  oxides,  of  which  manganese  dioxide, 
or  the  black  oxide  of  manganese,  occurs  most  frequently. 

Compounds  of  Manganese  with  Oxygen. — With  oxygen 
it  forms  the  following  compounds:  manganous  oxide, 
MnO;  manganic  oxide,  Mn203;  manganoso-manganic  oxide, 
Mn304;  manganese  dioxide,  Mn02;  and  permanganic  an- 
hydride, Mn207. 

Comparison  of  Manganese  with  Aluminium  and  with 
Iron, — Manganese  presents  points  of  resemblance  with 
aluminium  and  iron.  Like  iron  it  forms  two  series  of 
salts,  the  manganous  and  manganic  series,  which  differ 
from  each  other  very  much  as  ferrous  and  ferric  salts  do. 
Like  iron,  also,  it  forms  an  oxide,  Mn304,  which  is 
analogous  to  the  magnetic  oxide  of  iron.  Unlike  iron,  it 
forms  the  dioxide  Mn02.  Like  iron,  it  forms  salts,  which 
are  derived  from  an  acid  of  the  formula  H2Mn04;  as,  for 
example,  potassium  manganate,  K2Mn04.  Unlike  iron,  it 
forms  salts  derived  from  an  acid  HMn04;  as,  for  example, 
2)otassium  permanganate,  KMn04. 

Formation  of  Manganous  Salts. — The  higher  oxides  of 
manganese  generally  yield  manganous  salts  when  heated 
with  the  ordinary  acids ;  the  action  being  accompanied  by 

390 


MANGANESE  DIOXIDE.  391 

loss  of  oxygen.  In  these  salts  the  metal  is  apparently 
bivalent.  The  use  of  manganese  dioxide  in  preparing 
oxygen  and  chlorine  has  been  described.  [Give  an  account 
of  the  changes  which  manganese  dioxide  undergoes  when 
treated  with  sulphuric  acid;  hydrochloric  acid;  when 
heated.  ] 

Manganese  Dioxide,  Mn02. — This  important  compound 
occurs  in  nature  in  considerable  quantity,  and  is  known 
as  pyrolusite  or  black  oxide  of  manganese.  The  chief 
application  of  the  dioxide  is  in  the  preparation  of  chlorine. 
It  is  also  used  for  making  oxygen,  and  for  the  purpose  of 
decolorizing  glass.  In  the  last  process  a  small  quantity  is 
added  to  the  molten  glass.  This  alone  would  give  the 
glass  an  amethyst  color.  Without  it  the  glass  would  be 
green.  One  color  counteracts  the  other,  and  the  glass 
appears  colorless. 

Weldon's  Process  for  the  Regeneration  of  Manganese 
Dioxide  in  the  Preparation  of  Chlorine. — In  the  prepara- 
tion of  chlorine  by  means  of  manganese  dioxide  and 
hydrochloric  acid  the  manganese  is  converted  into  man- 
ganous  chloride  which  is  practically  worthless.  Weldon 
has,  however,  devised  a  method  for  the  utilization  of  the 
waste-liquors  of  the  chlorine  factories.  When  manganous 
chloride  in  solution  is  treated  with  lime  the  correspond- 
ing hydroxide  is  precipitated : 


MnCl2  +  Ca(OH)2  =  Mn(OH)2       CaOl 


•2' 


and  when  this  hydroxide  mixed  with  lime  is  treated  with 
steam  and  air  oxidation  takes  place,  and  a  compound 
CaMn03  or  CaMn205  is  formed: 

Mn(OH)2  +  Ca(OH)9  +  0  =  CaMn03  +  2H20; 
2Mn(OH)2  +  Ca(OH)2  -f  20  =  CaMn205  -f  3H20. 


39*  INTRODUCTION   TO   CHEMISTRY. 

These  compounds  give  chlorine  when  treated  with,  hydro- 
chloric acid.  They  may  indeed  be  regarded  as  consist- 
ing of  lime  and  manganese  dioxide,  CaO.Mn02  and 
Ca0.2Mn02. 

Potassium  Permanganate,  KMn04. — This  salt  is  obtained 
from  potassium  manganate,  K2Mn04,  by  boiling  or  by 
passing  carbon  dioxide  into  it.  The  manganate  is  mad ^ 
by  treating  manganese  dioxide  with  potassium  hydroxide 
and  potassium  chlorate;  in  other  words,  by  oxidizing 
manganese  dioxide  in  the  presence  of  the  base,  potassium 
hydroxide.  The  reaction  is  represented  by  the  equation 

3Mn02  +  6KOH  +  KC103  =  3K2Mn04  -f-  KC1  +  3H20. 

The  permanganate  is  a  dark-colored,  crystallized  com- 
pound that  dissolves  in  water,  forming  a  deep  purple- 
colored  solution. 

EXPERIMENT  183. — In  a  small  porcelain  crucible  heat  5  grams 
powdered  manganese  dioxide,  5  grams  potassium  hydroxide,  and 
2£  grams  potassium  chlorate.  When  the  mass  has  turned  green, 
let  it  cool,  dissolve  in  water,  neutralize  most  of  the  alkali,  and 
boil.  The  green  substance  is  potassium  manganate.  The  color 
will  change  from  green  to  purple, 

Reduction  of  Potassium  Permanganate. — Potassium  per- 
manganate gives  up  its  oxygen  very  readily  and  changes 
to  a  hydroxide  of  manganese.  If  an  acid  is  present  the 
hydroxide  dissolves,  forming  a  colorless  solution.  When, 
therefore,  a  solution  of  potassium  permanganate  is  added 
to  an  acid  solution  containing  an  oxidizable  substance  it 
becomes  colorless. 

EXPERIMENT  184.— To  a  dilute  solution  of  ferrous  sulphate 
containing  free  sulphuric  acid  add  drop  by  drop  a  dilute  solution 
of  potassium  permanganate.  The  color  will  be  destroyed  as  long 
as  there  is  any  ferrous  sulphate  present. 

Add  some  permanganate  solution  to  a  solution  of  sulphur  di- 


CHROMIUM.  393 

oxide  in  water.     [What  would  you  expect  to  take  place  in  this 
case  ?] 

Add  some  comparatively  dilute  hydrochloric  acid  to  a  few  crys- 
tals of  potassium  permanganate  in  a  test-tube.  [What  do  you 
notice  ?  How  do  you  explain  the  change  ?] 

Comparison  of  Potassium  Permanganate  with  Potassium 
Perchlorate. — Potassium  permanganate,  KMn04,  is  anal- 
ogous to  potassium  perchlorate,  KC104 ,  not  only  in  com- 
position, but  in  its  general  properties. 

Chromium,  Cr  (At.  Wt.  52.1). — This  element  is  com- 
paratively rare,  and  occurs  almost  always  in  combination 
'with  oxygen  and  iron  as  chromic  iron.  This  mineral, 
whose  composition  is  represented  by  the  formula  FeO204 , 
may  be  regarded  as  the  iron  salt  of  an  acid  of  the  formula 
HCr02.  Replacing  two  atoms  of  hydrogen  of  this  acid  by 
one  of  iron,  we  should  have  a  compound  Fe(Cr02)2.  This 
is  analogous  to  spinel,  which  in  a  similar  way  is  regarded 
as  magnesium  aluminate  of  the  formula  Mg(A102)2. 

Compounds  of  Chromium. — The  principal  compounds  of 
chromium  with  which  we  have  to  deal  are  potassium 
chromate,  K2Cr04;  potassium  dichromale,  K2Cr207,  and 
other  salts  derived  from  chromic  acid.  There  are,  how 
ever,  salts  in  which  chromium  takes  the  part  of  a  metal, 
replacing  the  hydrogen  of  acids;  as,  for  example,  chromium 
sulphate,  O2(S04)3. 

Potassium  chromate,  K2Cr04,  is  formed  when  finely- 
powdered  chromic  iron  is  heated  with  potassium  carbonate 
and  potassium  nitrate. 

EXPERIMENT  185. — Powder  some  chromic  iron  very  fine.  Mix 
3  grams  each  of  potassium  hydroxide,  potassium  carbonate,  and 
potassium  nitrate.  Melt  in  an  iron  crucible,  using  the  blast-lamp, 
and  add  the  chromic  iron  a  little  at  a  time,  as  long  as  it  dis- 


394  INTRODUCTION    TO   CHEMISTRY. 

solves.  After  cooling  treat  the  mass  with  water,  when  a  yellow- 
colored  solution  will  be  formed.  Potassium  chromate  is  in  the 
solution.  Save  this. 

Potassium  Bichromate,  K2Cr207. — This  is  the  form  in 
which  chromium  is  most  frequently  met  with.  It  is  made 
from  the  chromate  by  adding  acetic  or  nitric  acid,  and 
forms  large  red  crystals  that  are  soluble  in  water.  The 
change  is  represented  thus: 

2K2Cr04  +  2HN03  =  2KN03  +  K2Cr207  +  H20. 

The  relation  between  the  chromate  and  the  dichromate 
will  be  more  readily  understood  by  considering  the  acids 
from  which  they  are  derived.  These  are  chromic  acid, 
H2Cr04,  and  dichromic  acid,  H2Cr207.  The  latter  may 
be  regarded  as  derived  from  the  former  by  loss  of  water : 

2H2CrO,  =  H2Cr207  +  H20. 

The  same  relation  exists  between  sulphuric  acid,  H2S04, 
and  disulphuric  or  fuming  sulphuric  acid,  H2S207. 

EXPERIMENT  186. — Concentrate  the  solution  of  potassium  chro- 
mate already  obtained  and  add  nitric  acid  enough  to  decompose 
the  unused  potassium  carbonate  and  give  the  solution  an  acid  re- 
action. The  color  will  change  from  yellow  to  red.  The  red  color 
indicates  the  presence  of  the  dichromate. 

When  a  solution  of  potassium  dichromate  is  treated  with 
potassium  hydroxide  until  the  color  becomes  pure  yellow, 
the  chromate  is  formed: 

K2Cr207  -f  2KOH  =  2K2Cr04  +  H20. 

EXPERIMENT  187. — Convert  10  to  20  grams  potassium  dichro- 
mate into  the  chromate  by  the  method  mentioned.  Evaporate  to 
crystallization. 

The  Chromate  and  Bichromate  are  good  Oxidizing 
Agents. — Both  the  chromate  and  the  dichromate  are  good 
oxidizing  agents. 


CHROMIUM   COMPARED   WITH  ALUMINIUM,  ETC.    395 

EXPERIMENT  188.— Treat  a  little  of  each  salt  in  a  test  tube  with 
concentrated  hydrochloric  acid.  [What  evidence  do  you  get  that 
the  salts  are  good  oxidizing  agents  ?] 

(1)  K2CrO4  +  8HC1  =  2KC1  +  CrCU  +  4H2O  +  301. 

(2)  K2Cr2O7  +  14HC1  =  2KC1  +  2CrCl3  +  7H2O  +  601. 

Insoluble  Chromates, — The  chromates  of  barium  and 
lead,  like  the  sulphates,  are  insoluble  in  water.  They  are 
yellow.  The  lead  salt  is  the  well-known  pigment  chrome- 
yellow. 

EXPERIMENT  189. — Add  a  little  of  a  solution  of  potassium 
chromate  or  dichromate  to  a  solution  of  a  barium  salt  and  of  a 
lead  salt. 

Chrome  Alum  is  a  salt  allied  to  ordinary  alum,  but  con- 
taining chromium  instead  of  aluminium.  Its  formula  is 
CrK(S04) ,  +  12  H20.  The  alums  have  analogous  formulas : 

Ordinary  alum A1K(S04)2  +  12H20 

Iron  alum FeK(S04)2  +  12H20 

Chrome  alum CrK(S04)2  -f  12H20 

Comparison  of  Chromium  with  Aluminium,  Iron,  and 
Sulphur. — In  its  general  chemical  conduct  chromium  is 
similar  to  aluminium  and  iron  on  the  one  hand;  while,  on 
the  other  hand,  its  resemblance  to  sulphur  is  unmistakable, 
as  is  seen  in  the  formation  of  the  acids,  chromic  and 
dichromic  acids,  which  are  analogous  to  sulphuric  and 
disulphuric  acids,  not  only  in  composition,  but  in  some  of 
their  properties.  [Are  the  lead  and  barium  salts  of  sul- 
phuric acid  soluble  or  insoluble  in  water  ?] 

In  its  conduct  towards  reagents  chromium  more  closely 
resembles  aluminium  than  iron.  It  forms  no  sulphide  and 
no  carbonate,  so  that  when  a  soluble  carbonate  or  sulphide 
is  added  to  a  solution  of  a  chromium  salt,  such  as  chrome 
alum,  the  hydroxide  is  precipitated,  as  in  the  case  of 
aluminium.  The  hydroxide  dissolves  in  caustic  soda  and 


39 6  INTRODUCTION    TO   CHEMISTRY. 

caustic  potash,  but  is  repreoipitated  when  the  solution  is 
boiled.  [How  do  aluminium  and  iron  hydroxides  act 
towards  caustic  soda  ?J 

EXPERIMENT  190. — To  a  solution  of  potassium  chromate  add 
some  rather  strong  hydrochloric  acid  and  a  little  alcohol.  On 
boiling  the  alcohol  takes  up  oxygen  from  the  chromate,  a  peculiar- 
smelling  substance,  aldehyde,  is  given  off,  and  the  solution  now 
contains  chromium  chloride,  CrCU.  The  solution  has  a  green 
color.  The  change  is  represented  thus  : 
2K2CrO<  +  3CoH8O  +  10HC1  =  4KC1  +  2CrCl3  +  3C2H4O  +  8H9O. 

Alcohol.  Aldehyde. 

To  separate  portions  of  the  diluted  solution  add  ammonium 
sulphide,  sodium  carbonate,  and  sodium  hydroxide.  The  reac- 
tions which  take  place  are  : 

2OC1,  +  3(NH4)2S  +  6H2O  =  2Cr(OH)8  +  6NH«C1  +  3HaS. 

2CrCU  +  3Na2C03  +  3H2O  =  2Cr(OH)3  +  GNaCl  +  8COa. 

CrCl3  +  3NaOH  =  Cr(OH)3  +  3NaCl. 

After  noticing  the  general  appearance  of  the  precipitate  formed 
with  caustic  soda,  add  an  excess  of  the  latter.  [Does  the  precip- 
itate dissolve  ?]  Boil  the  solution.  [What  takes  place  ?J 

Uranium,  U  (At.  Wt.  239.5). — This  element  occurs 
mostly  in  the  form  of  the  oxide  U308  known  as  pitch- 
blende. It  forms  salts  in  which  the  group  U02,  called 
uranyl,  takes  the  place  of  two  atoms  of  hydrogen;  as,  for 
example,  uranyl  nitrate,  U08(NOS)S;  uranyl  sulphate, 
U02(S04). 

Uranium  oxide,  U203,  conducts  itself  towards  bases  like 
an  acid,  forming  salts  called  uranates. 

Radium  and  Polonium. — Certain  products  obtained  from 
pitchblende  emit  rays  that  in  some  respects  resemble  the 
Roentgen  rays,  but  in  other  respects  differ  from  them. 
These  rays  pass  through  opaque  bodies  and  afterwards 
produce  impressions  upon  photographic  plates.  At  least 
two  such  substances  have  been  obtained.  These  have 
been  called  polonium  and  radium.  They  are  not  known 
in  pure  condition. 


CHAPTER   XXVIII. 
PALLADIUM.-PLATINUM.— GOLD. 

Palladium,  ruthenium,  and  rhodium  are  three  rare  ele- 
ments that  closely  resemble  one  another. 

Palladium  forms  with  hydrogen  a  compound  which  in 
,  general  has  the  properties  of  alloys.  It  has  the  composi- 
tion Pd2H,  and  contains  about  600  volumes  of  hydrogen 
to  1  volume  of  palladium.  The  properties  of  this  sub- 
stance have  led  to  the  view  that  hydrogen  has  metallic 
properties.  If  by  the  name  metal  is  meant  an  element 
that  forms  salts  with  acids,  then  it  may  be  said  that 
hydrogen  bears  to  other  metals  a  relation  similar  to  that 
which  carbonic  acid  bears  to  other  acids.  Acids  are  sim- 
ply salts  of  hydrogen,  and  other  metals  drive  out  the 
hydrogen.  Carbonates  are  in  the  same  way  decomposed 
by  all  other  acids.  The  study  of  liquid  hydrogen  has, 
however,  shown  that  this  element  has  nothing  in  common 
with  the  metals. 

Platinum,  osmium,  iridium,  and  gold  form  a  group  in 
which,  however,  the  three  first  mentioned  are  the  most 
closely  related.  Of  these  three,  platinum  is  the  best 
known. 

Platinum,  Pt  (At.  Wt.  194.8),  occurs  almost  always 
accompanied  by  iridium,  palladium,  rhodium,  ruthenium, 
and  osmium,  in  the  form  of  alloys.  The  ore  is  found  in 

397 


398  INTRODUCTION    TO   CHEMISTRY. 

the  Ural  Mountains,  in  California,  Australia,  and  a  few 
other  places.  It  is  prepared  by  treating  the  ore  with 
strong  aqua  regia,  which  dissolves  the  platinum,  together 
with  some  iridium.  The  chlorplatinic  acid,  H2PtCl6 ,  thus 
obtained  is  precipitated  by  means  of  ammonium  chloride, 
with  which,  as  with  potassium  chloride  (see  p.  318),  it 
forms  a  difficultly  soluble  compound,  (NH4)2PtCl6.  When 
this  is  heated  to  a  sufficiently  high  temperature  it  is  decom  - 
posed,  leaving  metallic  platinum  as  a  residue.  By  special 
methods  the  iridium  can  be  separated  from  it. 

Properties, — Platinum  is  a  grayish-white  metal,  with  a 
high  lustre.  Its  specific  gravity  is  21.15,  it  being  one  of 
the  heaviest  substances  known.  The  specific  gravity  of 
iron  is  7.8,  that  of  lead  11.4,  and  that  of  lithium  0.59. 
In  other  words,  a  piece  of  platinum  weighs  nearly  three 
times  as  much  as  a  piece  of  iron  of  the  same  dimensions, 
and  nearly  twice  as  much  as  a  piece  of  lead  of  the  same 
dimensions.  Platinum  is  not  dissolved  by  hydrochloric, 
nitric,  or  sulphuric  acid;  but  aqua  regia  dissolves  it,  form- 
ing chlorplatinic  acid,  H2PtCl6.  Fusing  caustic  alkalies 
attack  it;  sodium  carbonate  does  not.  It  does  not  change 
in  the  air,  and  does  not  melt  except  in  the  flame  of  the 
oxyhydrogen  blowpipe.  It  resists  the  action  of  most  sub- 
stances. These  properties  make  it  extremely  valuable  to 
the  chemist.  Platinum  crucibles  and  evaporating-dishes, 
foil,  and  wire  are  constantly  used  in  the  laboratory,  and  it 
is  difficult  to  see  how  we  could  get  along  without  them. 
Large  retorts  of  platinum  are  used  for  the  purpose  of  con- 
centrating sulphuric  acid  and  distilling  it. 

Alloys  of  Platinum. — The  only  alloy  of  platinum  of  im- 
portance is  that  which  it  forms  with  iridium.  A  small 
percentage  of  this  metal  diminishes  the  malleability  of 
platinum  very  markedly,  and  makes  it  brittle;  but  increases 


GOLD.  399 

its  power  of  resistance  to  the  action  of  reagents.  An  alloy 
of  90  per  cent  platinum  and  10  per  cent  iridium  has  been 
adopted  by  the  French  Government  as  the  best  material 
from  which  to  make  normal  meters.  This  alloy  is  very 
hard,  as  elastic  as  steel,  more  difficultly  fusible  than 
platinum,  entirely  unchangeable  in  the  air,  and  is  capable 
of  a  high  polish. 

Chlorplatinic  Acid,  H2PtCl6,  is  made  by  dissolving  the 
metal  in  aqua  regia  and  evaporating  off  the  acids.  It  dis- 
solves in  water,  forming  a  yellowish-red  solution,  vhich  is 
used  in  the  laboratory  for  the  purpose  of  precipitating 
potassium  from  its  solutions,  as  the  salt  potassium  chlor- 
platinate,  K2PtCl6,  is  difficultly  soluble  in  water.  The 
corresponding  sodium  salt,  Na2PtCl6  +  6H20,  is  easily 
soluble  in  water. 

Gold,  Au  (At.  Wt.  197.2). — According  to  the  arrange- 
ment of  the  elements  in  the  periodic  system  gold  falls  in 
the  same  group  with  copper  and  silver,  with  which  it  has 
some  points  of  resemblance.  It  forms  more  properly  the 
connecting  link  between  the  platinum  group  and  the 
members  of  the  second  and  third  groups. 

Forms  in  which  Gold  occurs  in  Nature. — Gold  is  gen- 
erally found  in  nature  in  the  native  condition — a  fact 
which  is  undoubtedly  due  to  its  chemical  inactivity.  That 
which  is  found  in  nature  is  never  pure,  but  contains  silver, 
and  also,  in  different  localities,  iron,  copper,  and  other 
metals.  It  is  also  found  to  some  extent  in  combination 
with  tellurium  in  the  compounds  AuTe2  and  (AuAg)2Te3. 
Native  gold  is  frequently  found  enclosed  in  quartz,  or 
more  commonly  in  quartz  sand.  The  principal  localities 
in  which  it  is  found  are  California  and  some  of  the  other 
Western  States,  and  Australia,  Hungary,  Siberia,  and 
Africa. 


400  INTRODUCTION   TO  CHEMISTRY 

Metallurgy  of  Gold. — From  the  chemical  point  of  view 
the  metallurgy  of  gold  is  in  general  very  simple.  There 
are  two  kinds  of  gold-mining — called  placer* -mining  and 
vein-mining.  In  the  former  the  earth  and  sand  that  con- 
tain gold  are  washed  with  water,  which  carries  away  the 
lighter  particles,  and  leaves  the  gold  mixed  with  other  heavy 
materials.  This  mixture  is  then  treated  with  mercury., 
which  forms  an  amalgam  with  the  gold,  as  it  does  with 
silver,  and  when  this  is  placed  in  a  retort  and  heated,  the 
mercury  passes  over  leaving  the  gold  behind.  If  silver 
is  present,  as  is  frequently  the  case,  this  is  separated  with 
the  gold.  In  vein-mining  the  gold  ores  are  taken  out  of 
veins  in  the  earth,  and  the  gold  separated  by  grinding  the 
ores  and  treating  them  with  mercury,  as  in  the  last  stage 
of  placer-mining.  Hydraulic  mining  is  a  modification  of 
ordinary  placer-mining.  It  consists  in  forcing  water  under 
pressure  against  the  sides  of  hills  and  mountains  in  which 
gold  occurs  loosely  mixed  with  the  earth.  The  earth  is 
thus  carried  away  and  the  heavier  gold  is  deposited  in 
sluices. 

From  the  ores  gold  can  be  extracted  by  chlorine  and  Ly 
potassium  cyanide. 

The  chlorination  process  consists  in  subjecting  the  finely- 
divided  ore  in  suspension  in  water  to  the  action  of  chlorine 
from  bleaching-powder.  From  the  solution  thus  obtained 
the  gold  is  precipitated  in  the  metallic  form. 

The  cyanide  process  is  based  upon  the  fact  that  gold  in 
finely-divided  condition  dissolves  in  a  solution  of  potassium 
cyanide.  From  the  solution  the  gold  can  be  separated  by 
zinc  or  electrolytically. 

The  gold  obtained  as  above  is  not  pure.  It  can  be 
separated  from  silver  by  dissolving  it  in  aqua  regia, 
evaporating  so  as  to  drive  off  the  nitric  acid,  then  diluting, 

*  Pronounced  plfts'er. 


GOLD.  4°! 

and  treating  with  a  reducing  agent,  when  metallic  gold  is 
precipitated.  Thus  when  ferrous  sulphate  is  used  the  fol- 
lowing reaction  takes  place: 

3FeS04  +  AuCl3  =  Fe2(S04)3  +  FeCl3  -f  Au. 

Another  method  of  separating  silver  from  an  alloy  with 
gold  consists  in  treating  the  metal  with  nitric  acid  or  with 
boiling  concentrated  sulphuric  acid,  which  dissolves  the 
silver  and  leaves  the  gold.  This  process  is  not  satisfac- 
tory, however,  unless  the  amount  of  gold  in  the  alloy  is 
less  than  25  per  cent.  If  the  proportion  of  gold  is  greater 
than  this,  the  alloy  is  melted  with  silver  enough  to  bring 
the  percentage  of  gold  down  to  that  mentioned.  This  is 
known  as  "  quartation." 

Properties, — Gold  is  a  yellow  metal  with  a  high  lustre. 
It  is  quite  soft  and  extremely  malleable,  so  that  it  is  possi- 
ble to  make  from  it  sheets  the  thickness  of  which  is  not 
more  than  0.000002  millimetre.  Thin  sheets  are  trans- 
lucent, and  the  transmitted  light  appears  green.  Its 
specific  gravity  is  19.3;  its  melting-point  higher  than  that 
of  copper,  being  about  1200°.  It  ciystallizes  in  the  reg- 
ular system.  Gold  combines  directly  with  chlorine,  but 
not  with  oxygen.  The  three  acids,  hydrochloric,  nitric, 
and  sulphuric,  do  not  act  upon  it ;  but  aqua  regia  dissolves 
it,  forming  chlorauric  acid,  HAuCl4.  Molten  caustic 
alkalies  and  their  nitrates  act  upon  it,  probably  in  conse- 
quence of  the  tendency  to  form  aurates. 

Alloys  of  Gold. — The  principal  alloy  of  gold  is  that 
which  it  forms  with  copper.  The  standard  gold  coin  of 
the  United  States  contains  nine  parts  of  gold  to  one  of 
copper.  The  composition  of  gold  used  for  jewelry  is 
usually  stated  in  terms  of  carats.  Pure  gold  is  24-carat 
gold;  20-carat  gold  contains  20  parts  of  gold  and  4  parts 


402  INTRODUCTION   TO   CHEMISTRY. 

of  copper;  18-carat  gold  contains  18  parts  of  gold  and 
parts  of  copper,  etc.  Copper  gives  gold  a  reddish  color,  6 
and  makes  it  harder  and  more  easily  fusible.  Gold  is  also 
alloyed  with  silver;  and  the  alloy  with  mercury,  known  as 
gold-amalgam,  is  extensively  used  in  the  processes  for  ex- 
tracting gold  from  its  ores. 

Chlorides  of  Gold. — Auric  chloride,  AuCl3,  is  formed  by 
heating  gold  in  chlorine.  If  this  is  heated  in  an  atmos- 
phere of  carbon  dioxide,  it  is  decomposed  into  aurous 
chloride,  AuCl,  and  chlorine.  When  treated  with  a  solu- 
tion of  stannous  chloride  a  solution  of  auric  chloride  gives 
a  purple-colored  precipitate,  known  as  the  purple  of 
Cassius,  which  appears  to  consist  of  finely -divided  gold. 


CHAPTER   XXIX. 
SOME    FAMILIAR   COMPOUNDS   OF   CARBON. 

Organic  Chemistry. — When  the  compounds  that  are 
obtained  from  plants  and  animals  were  first  studied,  they 
were  supposed  to  be  entirely  different  from  the  compounds 
obtained  from  the  inorganic,  or  mineral,  constituents  of 
the  earth.  The  former  were  called  organic  compounds 
because  they  were  obtained  from  organized  things ;  while 
the  latter  were  called  inorganic  compounds.  Organic 
compounds  were  the  subject  of  Organic  Chemistry,  and 
inorganic  compounds  formed  the  subject  of  Inorganic 
Chemistry.  These  names  are  still  in  use,  though  they 
have  lost  their  original  significance.  Organic  Chemistry 
now  means  only  the  Chemistry  of  the  Compounds  of  Carbon. 

Occurrence  of  the  Compounds  of  Carbon. — The  com- 
pound of  carbon  that  occurs  most  widely  distributed  in 
nature  is  carbon  dioxide.  This,  as  has  been  pointed  out, 
is  the  starting-point  of  all  life  on  the  globe.  All  living 
things  are  formed  from  it  either  directly  or  indirectly. 
Attention  has  been  called  to  the  fact  that  starch  and 
cellulose  are  the  principal  compounds  found  in  plants,  and 
that  fats,  albumin,  and  fibrin  are  the  most  common  sub- 
stances found  in  animals. 

Formation  of  Hydrocarbons. — Certain  natural  processes 
which  are  not  thoroughly  understood  have  given  rise  to 

403 


404  INTRODUCTION    TO   CHEMISTRY. 

the  formation  of  a  complex  mixture  of  organic  com- 
pounds, principally  hydrocarbons,  in  petroleum.  One  of 
the  processes  involved  in  the  formation  of  these  hydro- 
carbons appears  to  be  the  action  of  water  on  metallic 
carbides  (see  Marsh-gas  or  Methane). 

Distillation  of  Coal. — The  destructive  distillation  of  coal 
for  the  purpose  of  making  illuminating-gas,  and  the 
formation  of  coal-tar,  have  already  been  referred  to. 
Coal-tar  is  one  of  the  most  important  sources  of  compounds 
of  carbon.  The  hydrocarbons  benzene,  C6H6,  toluene, 
C7II8,  xylene,  C8H10,  naphthalene,  C10H8,  anthracene, 
CUH10,  etc.,  are  obtained  from  this  source. 

Distillation  of  Wood. — Wood  is  heated  in  closed  vessels 
mostly  for  the  purpose  of  making  charcoal,  as  already 
explained.  Among  the  products  obtained  from  this  source 
are  wood-spirit,  or  methyl  alcohol,  and  pyroliyneous  acid, 
or  acetic  acid.  Large  quantities  of  acetic  acid  are  prepared 
in  this  way. 

Distillation  of  Bones. — In  order  to  make  bone-black, 
bones  are  subjected  to  destructive  distillation.  The  oil 
which  passes  over  is  collected  and  known  as  bone-oil. 
This  is  the  source  of  a  large  number  of  compounds  which 
are  of  special  interest  on  account  of  their  connection  with 
the  valuable  alkaloids  quinine,  morphine,  etc. 

Fermentation. — A  number  of  the  most  important  com- 
pounds of  carbon  are  formed  by  a  process  known  as  fermen- 
tation. This  is  a  general  term  meaning  any  process  in 
which  a  chemical  change  is  effected  by  means  of  minute 
animal  or  vegetable  organisms.  The  best -known  example 
of  fermentation  is  that  of  sugar,  which  gives  rise  to  the 
formation  of  ordinary  alcohol 


HYDROCARBONS.  405 

Classes  of  Compounds  of  Carbon. — The  chief  classes  of 
these  compounds  are  the  hydrocarbons  ;  the  alcohols  ;  the 
aldehydes  ;  the  acids ;  the  ethers ;  and  the  etJiereal  salts. 
First  a  few  of  the  best-known  examples  of  each  of  these 
classes  will  be  taken  up,  and  afterwards  some  other  familiar 
compounds  which  do  not  belong  to  any  one  of  these  classes. 

HYDROCARBONS. 

Compounds  of  Carbon  and  Hydrogen. — It  is  not  an  easy 
matter  to  effect  combination  between  carbon  and  hydrogen 
in  the  laboratory  except  in  a  few  simple  cases.  In  nature 
processes  are  in  operation  which  give  rise  to  the  formation 
of  a  large  number  of  compounds  containing  these  elements; 
and,  further,  in  the  manufacture  of  illuminating-gas  from 
coal  the  conditions  are  such  as  to  cause  the  combination 
of  carbon  and  hydrogen,  several  interesting  compounds 
being  thus  formed.  There  are  no  other  two  elements 
which  combine  with  each  other  in  as  many  different  pro- 
portions as  carbon  and  hydrogen.  The  compounds  thus 
formed  are  known  as  hydrocarbons.  The  number  of 
hydrocarbons  known  is  very  great,  being  somewhere  near 
two  hundred.  Fortunately,  investigation  has  shown  that 
quite  simple  relations  exist  between  these  compounds;  and 
hence,  though  the  number  is  large,  the  study  is  not  as 
difficult  as  might  be  expected. 

Petroleum  is  an  oily  liquid  found  in  many  places  in  the 
earth  in  large  quantity,  particularly  in  Pennsylvania  and 
the  Caucasus.  In  the  earth  it  contains  both  gases  and 
liquids.  When  it  is  brought  into  the  air,  the  pressure 
being  removed,  the  gases  are  given  off.  There  are  several 
gaseous  hydrocarbons  given  off,  and  a  large  number*  of 
liquids  left  behind. 

Refining  of  Petroleum. — The  vapors  from  petroleum 
when  mixed  with  air  are  explosive,  and  the  thicker  liquids 


4°6  INTRODUCTION   TO   CHEMISTRY. 

clog  the  lamps  and  wicks. .  Therefore  these  must  be 
removed  before  the  oil  is  fit  for  household  use.  This  is 
done  by  (1)  distilling,  (2)  washing  with  sulphuric  acid, 
(3)  washing  with  alkali,  and  (4)  washing  with  water.  The 
product  thus  prepared  is  called  kerosene. 

In  refining  petroleum  a  number  of  products  are  obtained 
which  cannot  be  used  in  lamps.  Those  which  are  lighter 
than  kerosene,  that  is  to  say  those  which  boil  at  a  lower 
temperature,  are  known  as  gasoline,  naphtha,  benzine,  etc. 
From  the  heavier  portions,  or  those  which  boil  at  higher 
temperatures  than  kerosene,  lubricating  oils  and  paraffin 
are  made.  Each  of  these  substances  is  a  mixture  of  several 
chemical  compounds. 

Hydrocarbons  contained  in  Petroleum. — The  simplest 
hydrocarbon  contained  in  petroleum  is  methane,  or  marsh- 
gas,  CH4;  the  next  has  the  composition  C2H6,  the  next 
C3II8,  etc.  It  will  be  seen  that,  as  far  as  composition  is 
concerned,  these  compounds  bear  a  simple  relation  to  one 
another.  They  are  the  first  members  of  a  series  the  names 
and  symbols  of  the  first  eight  members  of  which  are  given 
below : 

CH4,    Methane,  or  Marsh-gas; 

C2H6,  Ethane; 

C3H8,   Propane; 

C4H10,  Butane; 

C.H12,  Pentane; 

C6HU,  Hexane; 

C7H16,  Heptane; 

C8H18,  Octane. 

Homology. — The  first  member  of  the  series  differs  from 
the  second  by  CH2;  there  is  also  this  same  difference,  in 
general,  between  any  two  consecutive  members  of  the 
series.  This  relation  is  known  as  homology  f  and  such  a 


HYDROCARBONS.  4°7 

series  as  an  homologous  series.  Carbon  is  distinguished 
from  all  other  elements  by  its  power  to  form  homologous 
series. 

The  Ethylene  Series  of  Hydrocarbons, — Besides  the  series 
above  mentioned,  which  is  known  as  the  marsh-gas  series, 
there  are  other  homologous  series  of  hydrocarbons.  There 
is  one  beginning  with  ethylene,  C2H4 ,  examples  of  which 
are 

Ethylene,  C2H4; 
Propylene,  C3H6; 
Butylene,  C4H8. 

The  Acetylene  Series. — There  is  a  series  beginning  with 
acetylene,  examples  of  which  are 

Acetylene,  C2H2; 
Allylene,  03H4. 

The  Benzene  Series. — Another  series  begins  with  ben- 
zene, 06H6.  Some  of  the  members  of  this  series  are 

Benzene,  C6H6; 
Toluene,  C7H8; 
Xylene,  C8H10. 

Marsh-gas,  Methane,  Fire-damp,  CH4. — Marsh-gas  is 
found  in  nature  in  petroleum,  and  is  given  off  when  the 
oil  is  taken  out  of  the  earth,  and  the  pressure  is  removed. 
It  is  formed,  as  the  name  implies,  in  marshes,  as  the 
product  of  a  reducing  process.  Vegetable  matter  is  com- 
posed of  carbon,  hydrogen,  and  oxygen.  When  it  under- 
goes decomposition  in  the  air  in  a  free  supply  of  oxygen, 
the  final  products  formed  are  carbon  dioxide  and  water. 
When  the  decomposition  takes  place  without  access  of 
oxygen,  as  under  water,  marsh-gas,  which  is  a  reduction- 


408  INTRODUCTION   TO  CHEMISTRY. 

product,   is  formed.     The  gas  can  be  made  by  treating 
aluminium  carbide,  03A14,  with  water: 


C3A14  +  mi20  =  3CH4  +  4A1(OH)3. 

Marsh-gas  is  met  with  in  coal-mines,  and  is  known  to 
the  miners  as  fire-damp,  "  damp  "  being  the  general  name 
applied  to  a  gas,  and  the  name  fire-damp  meaning  a  g}i,s 
that  burns.  To  prepare  it  in  the  laboratory,  it  is  most 
convenient  to  heat  a  mixture  of  sodium  acetate  and  quick- 
lime. The  change  which  takes  place  will  be  most  readily 
understood  by  considering  it  as  a  simple  decomposition  of 
acetic  acid.  Acetic  acid  has  the  formula  C2H402.  When 
heated  alone,  it  boiis  and  does  not  suffer  decomposition. 

If  it  is  converted  into  a  salt,  and  heated  in  the  presence 
of  a  base,  it  breaks  up  into  marsh-gas  and  carbon  dioxide  : 

0,11.0,  =  en,  +  co,. 

The  carbon  dioxide,  which  forms  salts  with  bases,  does  not 
pass  off,  but  remains  behind  in  the  form  of  a  salt  of  car- 
bonic acid. 

Marsh-gas  is  a  colorless,  transparent,  tasteless,  inodorous 
gas.  It  is  slightly  soluble  in  water.  It  burns,  forming 
carbon  dioxide  and  water.  When  mixed  with  air,  the 
mixture  explodes  if  a  flame  or  spark  comes  in  contact  with 
it.  This  is  one  of  the  causes  of  the  explosions  which  so 
frequently  occur  in  coal-mines.  To  prevent  these  explo- 
sions a  special  lamp  was  invented  by  Sir  Humphry  Davy, 
which  is  known  as  Davy's  safety  -lamp  (p.  194). 

Substitution-products  of  the  Hydrocarbons.  —  Marsh-gas 
and  other  hydrocarbons  undergo  change  when  treated  with 
chlorine  and  bromine.  The  change  consists  in  the  substi- 
tution of  one  or  more  atoms  of  chlorine  or  of  bromine  for 
the  same  number  of  atoms  of  hydrogen.  In  the  case  of 


HYDROCARBONS.  409 

marsh-gas  and   chlorine  the  possible  changes  are  repre- 
sented as  below  : 

CH4  +  C12  =  CH3C1  +  HC1; 
CH3C1  +  C12  =  CH2C12  -f  HOI; 
CH2C12  +  C12  =  CHC13  +  HOI; 
CHC13  +  C12  =  001,  +  HOI. 

All  the  products  represented  are  known. 

Chloroform,  CHC13.  —  Chloroform  can  be  made  as  above 
indicated,  but  it  is  made  on  the  large  scale  by  treating 
alcohol  (which  see)  or  acetone  (which  see)  with  bleaching- 
powder.  It  is  a  heavy  liquid  with  an  ethereal  odor  and  a 
somewhat  sweet  taste.  It  is  one  of  the  most  valuable 
anaesthetics,  though  there  is  some  danger  attending  its  use. 

lodoform,  CHI3.  —  This  compound,,  like  chloroform,  is  a 
substitution-product  of  marsh-gas.  It  is  made  by  bring- 
ing together  alcohol,  an  alkali,  and  iodine.  It  is  a  solid 
substance,  soluble  in  alcohol  and  ether,  but  insoluble  in 
water.  It  crystallizes  in  six-sided  yellow  plates.  It  is 
extensively  used  as  a  dressing  for  wounds  in  surgery. 

Ethylene,  Olefiant  Gas,  C2H4.  —  This  hydrocarbon  is 
formed  by  heating  a  mixture  of  ordinary  alcohol  and  con- 
centrated sulphuric  acid.  The  reaction  is  represented 

thus: 


C20  =  H20  +  C3H4. 

Alcohol.  Ethylene. 

Ethylene  is  a  colorless  gas,  which  can  be  condensed  to 
a  liquid.  It  burns  with  a  luminous  flame.  With  oxygen 
it  forms  an  explosive  mixture. 

Acetylene,  C2H2.  —  Acetylene  is  formed  when  a  current 
of  hydrogen  is  passed  between  carbon  poles,  which  are  in- 
candescent in  consequence  of  the  passage  of  n  powerful 


4io 


INTRODUCTION    TO   CHEMISTRY. 


electric  current.  In  this  case  carbon  and  hydrogen  com- 
bine directly.  It  is  obtained  on  the  large  scale  by  treating 
calcium  carbide  (which  see)  with  water: 

CaC2  -fc  2H20  =  C2H2  +  Ca(OH)2. 

ALCOHOLS. 

Methyl  Alcohol,  Wood-spirit,  CH40. — This  is  formed  in 
the  distillation  of  wood,  and  must  be  separated  from  the 
other  products  which  are  formed  at  the  same  time.  It 
has,  when  pure,  a  pleasant  odor  and  taste,  and  acts  upon 
the  animal  system  very  much  as  ordinary  alcohol  does.  It 
burns  without  giving  light  or  smoke,  and  may  therefore 
be  used  in  lamps  for  heating-purposes  as  ordinary  alcohol 
is.  It  is  used  in  the  manufacture  of  varnishes. 

Ethyl  Alcohol,  Spirits  of  Wine,  C2H60.—  This  well-known 
substance  is  formed  by  the  fermentation  of  grape-sugar  or 

glucose.  C  f  HflO^ 

y    \9~  ^ 

EXPERIMENT  191. — Dissolve  about  150  grams  of  commercial 
grape-sugar  in  1£  litres  of  water  in  a  flask.  Connect  the  flask  by 
means  of  a  bent  glass  tube  with  a  cylinder  or  bottle  containing 


FIG.  58. 

clear  lime-water.  The  vessel  containing  the  lime-water  must  be 
provided  with  a  cork  with  two  holes.  Through  one  of  these 
passes  the  tnbe  from  the  fermentation-flask ;  through  the  other 
a  tube  connecting  with  a  vessel  containing  solid  caustic  potash, 


ALCOHOLS.  4" 

the  object  of  which  is  to  prevent  the  air  from  acting  upon  the 
lime-water.  The  arrangement  of  the  apparatus  is  shown  in 
Fig.  58.  Now  add  to  the  solution  of  grape-sugar  a  little  fresh 
brewers'  yeast ;  close  the  connections  and  allow  to  stand.  Soon 
an  evolution  of  gas  will  begin,  and,  as  this  passes  through  the 
lime-water,  a  precipitate  will  be  formed  which  can  be  shown  to 
be  calcium  carbonate. 

What  Change  takes  Place  in  the  Sugar? — If  the  solu- 
tion in  the  flask  is  examined  carefully  it  will  be  found  to 
contain  alcohol  and  no  sugar.  Grape-sugar  has  the  com- 
position expressed  by  the  formula  06H1206.  By  fermenta- 
tion it  is  decomposed,  forming  alcohol,  C2H60,  and  carbon 
dioxide,  C02,  thus: 

06H1206  =  2C2H60  +  200,. 

What  Causes  the  Change  ? — It  has  been  found  that  the 
change  of  grape-sugar  is  caused  by  small  organized  bodies 
which  grow  in  the  solution.  These  bodies  are  contained 
in  ordinary  yeast. 

Germs  in  the  Air. — When  fruit-juices  that  contain  sugar 
are  exposed  to  the  air  they  undergo  fermentation  without 
the  addition  of  yeast.  This  is  due  to  the  fact  that  the 
germs  or  seeds  of  the  bodies  that  cause  fermentation  are 
everywhere  floating  in  the  air.  Hence  when  a  liquid  in 
which  these  seeds  can  grow  is  exposed  to  the  air,  the 
bodies  are  formed  and  fermentation  takes  place. 

Different  Kinds  of  Fermentation. — The  fermentation 
which  yields  alcohol  is  only  one  of  many  kinds.  Among 
the  others  are:  (1)  lactic-acid  fermentation,  which  takes 
place  in  the  souring  of  milk;  and  (2)  acetic-acid  fermenta- 
tion, which  causes  the  transformation  of  alcohol  into  acetic 
acid.  The  latter  ferment  is  contained  in  "mother  of 
vinegar." 


412  INTRODUCTION   TO  CHEMISTRY. 

Distillation  of  Fermented  Liquids.  —  In  order  to  get  the 
alcohol  from  liquids  which  have  undergone  fermentation 
they  must  be  distilled.  For  this  purpose  very  perfect 
forms  of  stills  have  been  devised,  so  that  the  alcohol  passes 
over  nearly  free  from  other  substances.  Usually  it  con- 
tains impurities  known  aa  fusel  oil. 

Properties  of  Alcohol.  —  Pure  ethyl  alcohol  has  a  peculiar, 
pleasant  odor.  It  remains  liquid  at  very  low  temperatures, 
but  has  been  converted  into  a  solid  at  a  temperature  of 
-  130.5°.  It  burns  with  a  flame  which  does  not  deposit 
soot,  and  was  hence  formerly  much  used  in  laboratories 
for  heating  purposes,  and  is  still  used  where  gas  cannot  be 
obtained.  Its  effects  upon  the  human  system  are  well 
known.  It  intoxicates  when  taken  in  dilute  form,  while 
in  large  doses  it  is  poisonous.  It  lowers  the  temperature 
of  the  body  when  taken  internally,  although  it  causes  a 
sensation  of  warmth. 

Uses  of  Alcohol.  —  Alcohol  is  the  principal  solvent  for 
organic  substances.  It  is  hence  extensively  used  in  the 
arts,  as  in  the  manufacture  of  varnishes,  perfumes,  and 
tinctures  of  drugs.  Most  beverages  in  use  owe  their  in- 
toxicating-power  to  the  presence  of  alcohol.  The  milder 
forms  of  beer  contain  from  2  to  3  per  cent;  light  wines 
about  8  per  cent;  while  whiskey,  brandy,  etc.,  sometimes 
contain  as  much  as  60  io  75  per  cent. 


Glycerin,  C3H803.  —  Glycerin  is  an  alcohol  which  occurs 
very  widely  distributed  as  a  constituent  of  fats.  The 
relation  it  bears  to  the  fats  will  be  explained  when  the 
acids  which  enter  into  the  fats  are  taken  up.  It  is  obtained 
from  the  fats  by  boiling  them  with  an  alkali  like  caustic 
soda  or  caustic  potash,  or  by  heating  with  steam. 


ALDEHYDES.  4*3 

Properties.  —  Glycerin  is  a  thick,  colorless  liquid  with  a 
sweetish  taste.  It  attracts  moisture  from  the  air,  and  is 
hence  nsecf  to  keep  surfaces  moist. 


ALDEHYDES.  ^l 

Acetic  Aldehyde,  Ordinary  Aldehyde,  C2H4'0.  —  This 
compound  is  formed  by  oxidizing  ordinary  alcohol,  the 
change  being  represented  by  this  equation  : 

C2H60  +  0  =  C2H40  +  H20. 

EXPERIMENT  192.  —  In  a  small  flask  put  a  few  pieces  of  potassium 
dichromate,  KaOsOi  ,  and  pour  upon  it  a  few  cubic  centimetres  of 
moderately  concentrated  sulphuric  acid.  To  this  mixture  add 
slowly  a  few  cubic  centimetres  of  ordinary  alcohol.  Notice  the 
odor. 

Aldehyde  is  a  volatile  liquid  with  a  characteristic  pene- 
trating odor.  When  left  to  itself,  and  especially  when 
treated  with  a  number  of  other  things,  it  is  converted  into 
another  substance  of  the  same  composition.  This  is  called 
paraldehyde.  A  determination  of  the  molecular  weight  of 
the  substance  by  the  method  of  Avogadro  has  shown  that 
it  must  be  represented  by  the  formula  C6H1203.  The 
change  from  aldehyde  to  paraldehyde  must,  therefore,  be 
represented  thus: 

80.H.O  =  C6H1203. 

Paraldehyde  is  used  in  medicine. 

Chloral,  02C13HO,  is  a  compound  formed  by  the  action 
of  chlorine  on  alcohol.  It  is  related  to  aldehyde,  as 
chloroform  is  related  to  marsh-gas,  that  is  to  say,  it  is  a 
trichlorine  substitution-product.  It  is  a  colorless  liquid. 
With  water  it  forms  a  crystallized  compound,  chloral 
hydrate,  C201SHO  -f-  H20,  which  is  easily  soluble  in  water, 
and  crystallizes  from  the  solution  in  colorless  prisms. 
Taken  internally  in  doses  of  from  1.5  to  5  grams,  it 
produces  sleep.  In  larger  doses  it  acts  as  an  anaesthetic. 


4U  INTRODUCTION   TO  CHEMISTRY. 

ACIDS. 

Formic  Acid,  CH202. — This  acid  occurs  in  nature  in  red 
ants,  in  stinging-nettles,  in  the  shoots  of  some  of  the 
varieties  of  pine,  and  elsewhere.  It  is  a  colorless  liquid. 
Dropped  on  the  skin*  it  causes  pain  and  produces  blisters. 

Acetic  Acid,  C2H4O2. — This  is  the  acid  contained  in 
vinegar,  and  the  value  of  vinegar  is  due  to  its  presence. 
It  is  formed  from  alcoholic  liquids  by  exposing  them  to  the 
air,  in  consequence  of  the  presence  of  a  microscopic 
organism  which  is  contained  in  what  is  commonly  known 
as  "mother  of  vinegar."  The  formation  of  acetic  acid 
from  alcohol  is  due  to  the  action  of  oxygen  as  represented 
in  the  equation  ^  ^DH  *%l  ^&0\* 

02H60  +  02  =  C2H402  +  H20. 

Alcohol.  Acetic  acid. 

But  oxygen  alone  does  not  effect  the  change.  When  the 
ferment  is  present  the  oxidation  takes  place.  Acetic  acid 
is  also  obtained  by  distilling  wood.  Hence  the  names 
pyroligneous  acid  and  wood-vinegar. 

Properties, — Acetic  acid  is  a  clear,  colorless  liquid.  It 
has  a  very  penetrating,  pleasant,  acid  odor,  and  a  sharp 
taste.  The  pure  substance  acts  upon  the  skin  like  formic 
acid,  causing  pain  and  raising  blisters. 

Uses. — Acetic  acid  is  extensively  used,  chiefly  in  the 
dilute  form  known  as  vinegar.  It  is  used  in  calico-print- 
ing in  the  form  of  iron  and  aluminium  salts.  With  iron 
it  gives  hydrogen,  which  is  needed  in  the  manufacture  of 
certain  compounds  used  in  making  dyes. 

Salts  of  Acetic  Acid. — The  best-known  salts  of  acetic 
acid  are  lead  acetate,  Pb(02H302)2 ,  commonly  called  sugar 
of  lead ;  and  copper  acetate,  Cu(C2H302)2,  a  variety  of 
which  is  known  as  verdigris. 


ACIDS.  415 

Fatty  Acids. — Formic  and  acetic  acids  are  the  first 
members  of  an  homologous  series  (see  p.  406).  Some  of 
the  more  important  members  are  named  in  the  following 
table: 

0: 

Formic     acid CHaOa.-^ 

Acetic 


Propionic 

Butyric 

Palmitic 

Stearic 


C4H8( 

CTT 
l«tiS 

C 


If] 


They  are  called  fatty  acids  for  the  reason  that  many  of 
them  are  obtained  from  fats. 

Butyric  acid,  C4H802 ,  is  of  special  interest  because  it  is 
obtained  from  butter  by  boiling  with  caustic  potash.  It 
occurs  also  in  many  other  fats.  There  is  a  butyric-acid 
ferment  contained  in  putrid  cheese  which  has  the  "oower 
of  converting  sugar  into  butyric  acid. 

Palmitic  acid,  C16H3202,  is  obtained  from  many  fats,  but 
palm-oil  is  especially  rich  in  it. 

Stearic  acid,  C18H3602 ,  is  the  acid  contained  in  the  fat 
known  as  stearin.  The  so-called  "stearin  candles"  are 
made  of  a  mixture  of  palmitic  and  stearic  acids. 

Soaps. — Soaps  are  the  alkali  salts  of  the  acids  contained 
in  fats,  especially  of  palmitic  and  stearic .  acids.  Fats  are 
compounds  of  these  acids  with  glycerin.  When  the  fats 
are  boiled  with  an  alkali,  as  caustic  soda,  the  correspond- 
ing salts  of  the  acids  are  formed,  while  the  glycerin  is  set 
free.  The  palmitate  and  stearate  of  potassium  and  sodium 
are  the  soaps. 

EXPERIMENT  193. — In  an  iron  pot  boil  a  quarter  of  a  pound  of 
lard  with  a  solution  of  40  grams  caustic  soda  in  250  cc.  of  water 
for  an  hour  or  two.  After  cooling  add  a  strong  solution  of  so- 
dium chloride.  The  soap  formed  will  separate  and  rise  to  the 


416  '    INTRODUCTION   TO   CHEMISTRY. 

top  of  the  solution,  where  it  will  finally  solidify.     Dissolve  in 
water  some  of  the  soap  thus  obtained. 

Use  of  Soap. — The  cleansing  power  of  soap  depends  upon 
the  fact  that  it  removes  the  oily  film  on  the  surface  of  the 
skin  and  thus  facilitates  the  removal  of  the  foreign  sub- 
stances commonly  known  as  dirt. 

Action  of  Soap  on  Hard  Waters, — As  has  been  explained, 
a  hard  water  is  one  that  contains  salts  in  solution.  Tem- 
porary hardness  is  that  which  is  caused  by  calcium  car- 
bonate held  in  solution  in  the  water  by  carbon  dioxide. 
Permanent  hardness  is  caused  by  calcium  sulphate  or 
magnesium  salts.  The  calcium  and  magnesium  salts  of 
palmitic  and  stearic  acids  are  insoluble  in  water.  There- 
fore, when  soap  is  added  to  a  hard  water  these  insoluble 
salts  are  precipitated  and  give  the  water  a  hard  feeling. 
In  attempting  to  wash  the  hands  with  soap  in  a  hard  water 
they  become  covered  with  a  thin  layer  of  the  insoluble 
salts  which  prevents  them  from  rubbing  freely  over  each 
other,  and  makes  them  feel  sticky.  Before  the  soap  can 
do  any  good  all  the  lime-salt  must  be  precipitated.  The 
action  in  the  case  of  temporary  hardness  is  represented  by 
the  equation 

2NaC16H3100  +  CaCOs  =  Ca(C16H3102)2  +  Na2C03. 

Soap.  Calcium  palmitate. 

In  the  case  of  permanent  hardness  it  is  represented  by 
the  equation 

'    2NaC16H3102  +  CaS04  =  Ca(C16H3l02)2  +  Na2S04. 

EXPERIMENT  194. — Make  some  hard  water  by  passing  carbon 
dioxide  through  dilute  lime-water  until  the  precipitate  first  formed 
is  dissolved  again.  Filter.  Make  a  solution  of  soap  by  shaking 
up  a  few  shavings  of  soap  with  water.  Filter.  Add  the  solution 
of  soap  to  the  hard  water.  Is  a  precipitate  formed  ?  Rub  a 
piece  of  soap  between  the  hands  wet  with  the  hard  water. 


ACIDS.  417 

EXPERIMENT  195.— Make  some  hard  water  by  shaking  a  litre  or 
two  of  water  with  a  little  powdered  gypsum.  Perform  with  it  the 
same  experiments  as  those  first  performed  with  the  water  con- 
taining calcium  carbonate. 

Kelations  of  the  Soap  Industry  to  other  Industries. — A 
great  chemist  and  philosopher  has  said  that  the  quantity 
of  soap  used  in  a  country  is  a  measure  of  the  civilization 
of  that  country.  Certain  it  is  that  soap  is  only  used  by 
civilized  people,  and  that  by  them  it  is  used  in  enormous 
quantities.  In  many  farm-houses  a  primitive  method  for 
the  manufacture  of  soap  is  practised,  consisting  in  treating 
refuse  fats  with  the  lye  extracted  from  wood-ashes.  A 
soft  soapy  mass  is  thus  obtained  known  as  "soft-soap." 
Fats  form  the  starting-point  in  the  manufacture  of  all  soap. 
These  are  generally  treated  with  caustic  soda. 

Oxalic  Acid,  02H204. — This  acid  occurs  very  widely^dis- 
tributed  in  nature,  as  in  the  sorrels,  which  owe  their  acid 
taste  to  the  presence  of  acid  potassium  oxalate,  KC2H04; 
and  as  the  ammonium  salt  in  guano.  It  is  probably  one 
of  the  first  substances  formed  from  carbon  dioxide  in  the 
plant.  It  is  manufactured  by  heating  wood  shavings  or 
sawdust  with  caustic  soda  and  caustic  potash.  Oxalic  acid 
is  an  active  poison.  It  is  used  in  calico-printing,  and  in 
cleaning  brass  and  copper  surfaces. 

Lactic  Acid,  C3H603. — Lactic  acid  is  made  by  the  fer- 
mentation of  sugar  by  means  of  the  lactic-acid  ferment. 
The  reaction  effected  by  the  ferment  is  represented  by  the 
equation 

C6H1206  =  2C3H603. 

Malic  Acid,  C4H605, — This  acid  is  widely  distributed  in 
the  vegetable  kingdom,  as  in  apples,  cherries,  etc. 

Tartaric  Acid,  C4H606  — Tartaric  acid  occurs  widely  dis- 
tributed in  fruits,  sometimes  uncombined,  sometimes  in 


418  INTRODUCTION   TO   CHEMISTRY. 

the  form  of  the  potassium  or  calcium  salt;  as,  for  example, 
in  grapes,  berries  of  the  mountain-ash,  potatoes,  cucum- 
bers, etc.,  etc.  It  is  prepared  from  "  cream  of  tartar." 
This  is  acid  potassium  tartrate,  which  is  formed  when 
grape-juice  ferments. 

Citric  Acid,  C6H807. — Citric  acid,  like  malic  and  tartaric 
acids,  is  very  widely  distributed  in  nature  in  many  varieties 
of  fruit,  especially  in  lemons.  It  is  also  found  in  currants, 
whortleberries,  raspberries,  gooseberries,  etc.,  etc.  It  is 
prepared  from  lemon-juice:  100  parts  of  lemons  yield  5^ 
parts  of  the  acid.  It  is  a  solid,  crystallized  substance, 
soluble  in  water.  It  is  frequently  used  for  the  purpose  of 
making  lemonade  without  lemons,  and  there  is  no  objec- 
tion to  its  use  for  this  purpose. 

ETHERS. 

Ether,  C4H100. — Ordinary  ether  is  the  best-known  repre- 
sentative of  the  class  of  compounds  called  ethers.  It  is 
formed  from  ordinary  alcohol  by  treating  it  with  sulphuric 
acid  and  distilling.  The  result  of  the  action  which  takes 
place  is  represented  by  the  equation 

2C2H60  =  C4H100  +  H20. 

Alcohol.  Ether. 

Ether  is  a  liquid  which  boils  at  a  low  temperature  and 
takes  fire  and  burns  readily.  Inhaled  it  produces  insensi- 
bility to  pain.  It  is  therefore  called  an  anwsthetic. 

ETHEEEAL    SALTS. 

Action  of  Acids  upon  Alcohols. — When  an  acid  acts  upon 
an  alcohol  it  is  neutralized,  though  not  as  readily  as  when 
it  acts  upon  a  base.  The  product  is  a  substance  which 
resembles  a  salt  and  is  called  an  ethereal  salt.  Thus  when 
nitric  acid  acts  upon  alcohol  this  reaction  takes  place: 

C,H60  +  UNO,  =  C2H6N03  -f  H,0. 


ETHEREAL  SALTS.  419 

The  product  C2H5N03 ,  called  ethyl  nitrate,  is  an  ethereal 
salt.  The  alcohol  acts  as  if  it  were  a  substance  like  caustic 
potash  and  made  up  thus,  C2H5OH.  The  resemblance 
between  its  action  and  that  of  caustic  potash  is  shown  by 
the  equations 

KOH       +  HN03  =  KNO,       +  H20,  and 
02H5OH  +  HN03  =  C2H5N03  +  H20. 

Saponification. — When  an  ethereal  salt  is  boiled  with  a 
caustic  alkali  it  is  decomposed,  the  products  being  an 
alcohol  and  an  alkali  salt.  Thus  when  ethyl  nitrate  is 
boiled  with  caustic  potash,  potassium  nitrate  and  alcohol 
are  formed: 

02H5N03  +  KOH  =  C2H5OH  -f  KN03. 

This  process  is  called  saponification,  because  the  most 
important  example  is  furnished  by  soap-making. 

Fats. — The  fats  are  ethereal  salts  in  the  formation  of 
which  glycerin,  as  the  alcohol,  and  three  acids  take  part. 
The  three  acids  are  palmitic  and  stearic  acids,  already 
mentioned,  and  oleic  acid,  C18H3402.  Although  the  com- 
position of  these  substances  is  comparatively  complex,  the 
way  they  act  upon  one  another  is  simple,  and  is  the  same 
as  the  action  of  nitric  acid  upon  alcohol  in  forming  ethyl 
nitrate.  The  fats,  then,  are  the  palmitate,  stearate,  and 
oleate  of  glyceryl,  which  bears  to  glycerin  very  much  the 
same  relation  that  ethyl,  C2H5 ,  bears  to  alcohol.  When  a 
fat  is  boiled  with  caustic  soda,  glycerin  and  the  sodium 
salts  of  the  acids  contained  in  the  fat  are  formed. 

Butter  consists  of  ethereal  salts  of  glycerin  and  several 
fatty  acids,  among  which  are  palmitic,  stearic,  and  butyric. 
Oleomargarin  is  an  artificial  butter  made  from  other  fats 
than  that  of  milk. 


420  INTRODUCTION   TO  CHEMISTRY. 

Ethereal  Salts  as  Essences. — The  ethereal  salts  generally 
have  pleasant  odors,  and  it  is  to  their  presence  that  many 
fruits  owe  their  flavors.  Some  of  the  compounds  are  now 
made  artificially  and  used  instead  of  the  fruit-extracts. 
Thus  the  ethyl  salt  of  butyric  acid  is  used  under  the  name 
of  essence  of  pineapples,  and  the  amyl  salt  of  valeric  acid 
under  the  name  of  essence  of  apples. 

Nitroglycerin. — Among  the  more  important  ethereal 
salts  of  glycerin  are  the  nitrates.  Two  of  these  are 

r  o.N02 

known,  viz  ,  tlie  mono-nitrate,  C.H,  <  OH       ,  and  the  tri- 

(OH 

nitrate,  C3H5(O.N02)3,  the  latter  being  the  chief  con- 
stituent of  nitroglycerin.  Nitroglycerin  is  prepared  by 
treating  glycerin  with  a  mixture  of  concentrated  sulphuric 
and  nitric  acids.  It  is  a  pale  yellow  oil  which  is  insoluble 
in  water.  At  —  20°  it  crystallizes  in  needles.  It  explodes 
very  violently  by  concussion.  It  may  be  burned  in  an 
open  vessel,  but  if  heated  above  250°  it  explodes. 
Dynamite  is  infusorial  earth*  impregnated  with  nitro- 
glycerin. Nitroglycerin  is  the  active  constituent  of  a 
number  of  explosives. 

RELATIONS    BETWEEN"    THE    COMPOUNDS    CONSIDERED. 

Comparison  of  the  Formulas. — On  comparing  the  formu- 
las of  the  hydrocarbons  of  the  marsh-gas  series  (see  p.  406) 
with  those  of  the  simplest  alcohols  and  the  fatty  acids,  it 
will  be  seen  that  these  compounds  are  all  related  in  a 
simple  way.  Below  are  lists  of  a  few  of  the  hydrocarbons, 
alcohols,  and  acids: 

*  That  is  to  say,  earth  made  up  of  the  microscopic  flinty  shells 
which  constitute  the  fossil  remains  of  certain  minute  and  simple 
plants. 


ALCOHOLS.  421 

Hydrocarbons.  Alcohols.  Acids. 

'  GH4  OH40  CH202 

C2H6  C2H60  C2H402 

C3H8  C3H80  C3H602 

C4H10,  etc.  C4H100,  etc.  04H802,  etc. 

Each  of  these  series  is  an  homologous  series. 

Alcohols.  —  Alcohols  have  been  shown  to  be  derived  from 
the  hydrocarbons  by  the  replacement  of  one  or  more 
hydrogen  atoms  by  oxygen  and  hydrogen,  OH,  called 
hydroxyl,  or  from  water  by  replacing  one  of  the  hydrogen 
atoms  of  the  water  by  a  group  composed  of  carbon  and 
hydrogen.  An  alcohol,  then,  is  a  hydroxide,  just  as  a 
metallic  base  is;  only,  instead  of  consisting  of  a  metal  in 
combination  with  hydroxyl,  it  consists  of  a  compound  of 
carbon  and  hydrogen  in  combination  with  hydroxyl.  Thus  : 

Metallic  Bases.  Alcohols. 

K(OH)  CHS(OH) 

Na(OH)  C, 


More  Complex  Alcohols,  —  Just  as  lime  is  a  more  complex 
base  than  caustic  potash,  as  shown  by  the  formulas  KOH 
and  Ca02H2  or  Oa(OH)2,  so  there  are  more  complex 
alcohols  than  ordinary  alcohol.  A  good  example  is  fur- 
nished by  glycerin,  C3H803  ,  which  has  been  shown  to  be 
a  hydroxide  corresponding  to  aluminium  hydroxide, 
A1(OH)3,  a  fact  which  is  represented  by  the  formula' 
C3H5(OH)3.  It  may  be  called  glyceryl  hydroxide,  the 
complex,  C3H5  ,  being  known  as  glyceryl. 

Radicals  or  Residues.  —  The  compounds  of  hydrogen  and 
carbon  contained  in  the  alcohols  are  called  radicals  or 
residues.  We  may  say  that  an  alcohol  is  water  in  which 
half  of  the  hydrogen  has  been  displaced  by  a  radical, 


INTRODUCTION    TO   CHEMISTRY. 
HOH  C5H6OH 

Water.  Ordinary  alcohol. 

HOH  (  OH 

HOH  C8HJ  OH  =  C3H808. 

HOH  (  OH 

Water.  Glycerin. 

Acids.  —  Just  as  the  alcohols  have  been  shown  to  be 
derived  from  water,  so  the  organic  acids  have  been  shown 
to  be  derived  from  carbonic  acid.  The  carbonates  are 

derived  from  an  acid  of  the  formula  H2C03,  or  CO  j  ^  „. 

If,  in  this  acid,  a  hydroxyl  is  replaced  by  a  radical,  as,  for 
example,    by   ethyl,    C2H5,   a   substance   of   the   formula 

CO  -         *   or    C3H602  is  the  result.     If  methyl,  CH3  ,  is 


(  PIT 

introduced  in  place  of  ethyl,  the  product  is  CO  -j  ^rr3  or 

C2H402  ,  which  is  acetic  acid.     In  a  similar  way  all  the 
organic  acids  are  derived  from  carbonic  acid. 


CHAPTER   XXX. 
OTHER   COMPOUNDS  OF  CARBON. 

The  Carbohydrates. — The  carbohydrates  form  an  im- 
portant group  of  carbon  compounds  which  include  the 
*most  abundant  substances  found  in  the  vegetable  kingdom. 
Besides  carbon,  they  contain  hydrogen  and  oxygen  in  the 
proportions  to  form  water.  Hence  they  are  called  carbo- 
hydrates. The  chief  compounds  included  under  this  head 
are  grape-sugar  or  glucose,  cane-sugar,  starch,  cellulose, 
gum,  and  dextrin. 

Grape-sugar,  Glucose,  Dextrose,  C6H12Og.  —  Dextrose 
occurs  very  widely  distributed  in  plants,  particularly  in 
sweet  fruits.  It  is  found  also  in  honey  and,  further,  in 
the  liver  and  the  blood. 

Formation  of  Dextrose. — Dextrose  or  glucose  is  formed 
from  several  of  the  carbohydrates  by  boiling  with  dilute 
mineral  acids,  or  by  the  action  of  ferments.  Its  formation 
from  cane-sugar  takes  place  according  to  this  equation, 
equal  quantities  of  dextrose  and  levulose  being  formed : 

C12H2!0U  +  H,0  =  C,HB0.  +  0.1^0^ 

Cane-sugar.  Dextrose.  Levulose. 

Its  formation  from  starch  is  represented  by  this  equation : 
C,H1005  +  H20  =  C6H,,06. 

btarch.  Dextrose, 

423 


424  INTRODUCTION   TO   CHEMISTRY. 

Manufacture  of  Dextrose  or  Glucose. — Dextrose  is  pre- 
pared on  the  large  scale  from  corn-starcb  in  the  United 
States,  and  from  potato-starch  in  Germany.  The  change 
is  usually  effected  by  boiling  with  dilute  sulphuric  acid. 
The  acid  is  afterwards  removed  by  treating  with  chalk, 
and  filtering.  [Explain  how  this  removes  the  acid.  ]  The 
filtered  solutions  are  evaporated  either  to  a  syrupy  con- 
sistency, and  sent  into  the  market  under  the  names 
"glucose,"  "mixing-syrup,"  etc.;  or  to  dryness,  the 
solid  product  being  knoAvn  as  "grape-sugar." 

Properties. — Dextrose  crystallizes  from  concentrated 
solutions,  and  as  seen  in  commercial  "granulated  grape- 
sugar  "  looks  very  much  like  granulated  cane-sugar.  It  is 
sweet,  but  not  as  sweet  as  cane-sugar.  It  is  estimated 
that  the  sweetness  of  dextrose  is  to  that  of  cane-sugar  as 
3:5.  Under  the  influence  of  yeast  it  ferments,  yielding 
mainly  alcohol  and  carbon  dioxide.  Putrid  cheese  trans- 
forms it  into  lactic  acid,  and  then  into  butyric  acid. 

Levulose,  Fruit-sugar,  C6H1206. — This  form  of  sugar 
occurs  with  dextrose  in  fruits ;  and  is  formed  by  the  action 
of  dilute  acids  or  ferments  on.  cane-sugar,  which  breaks 
up  according  to  the  equation 

Ci2H22°n  +  H,°  =  C6HiA  +  C6HiA' 
Cane-sugar.  Dextrose.  Levulose. 

As  cane-sugar  is  found  in  unripe  fruits,  it  is  probable 
that  the  change  represented  in  the  equation  takes  place 
during  the  process  of  ripening. 

Cane-sugar,  C12H22On. — This  well-known  variety  of  sugar 
occurs  very  widely  distributed  in  nature — in  sugar-cane, 
sorghum,  the  Java  palm,  the  sugar-maple,  beets,  madder- 
root,  coffee,  walnuts,  hazel-nuts,  sweet  and  bitter  almonds; 
in  the  blossoms  of  many  plants,  etc. ,  etc. 


SUGAR.  425 

Sugar-refining.  —  Sugar  is  obtained  mainly  from  the 
sugar-cane  and  beets.  In  either  case  the  processes  of  ex- 
traction and  refining  are  largely  mechanical.  When  sugar- 
cane is  used,  this  is  macerated  with  water  to  dissolve  the 
sugar.  Thus  a  dark-colored  solution  is  obtained.  This 
is  evaporated,  and  then  passed  through  filters  of  bone-black 
by  which  the  color  is  removed.  The  clear  solution  is  then 
evaporated  in  open  vessels  to  some  extent;  and,  finally,  in 
large  closed  vessels  called  "vacuum-pans,"  from  which  the 
air  is  partly  exhausted,  so  that  the  boiling  takes  place  at  a 
lower  temperature  than  is  required  under  the  ordinary 
pressure  of  the  atmosphere.  The  mixture  of  crystals  and 
mother-liquors  obtained  from  the  "vacuum-pans"  is  freed 
from  the  liquid  by  being  brought  into  the  "centrifugals." 
These  are  funnel-shaped  sieves  which  are  revolved  rapidly, 
the  liquid  being  thus  thrown  by  centrifugal  force  through 
the  openings  of  the  sieve,  while  the  crystals  remain  behind 
and  are  thus  nearly  dried.  The  final  drying  is  effected  by 
placing  the  crystals  in  a  warm  room. 

Molasses. — The  mother-liquors  obtained  from  the  "cen- 
trifugals "  are  further  evaporated,  and  yield  lower  grades 
of  sugar;  and,  finally,  a  syrup  is  obtained  which  does  not 
crystallize.  This  is  molasses. 

Properties  of  Sugar. — Sugar  crystallizes  from  water  in 
large  well-formed  prisms.  When  heated  to  210°  to  220°, 
it  loses  water,  and  is  converted  into  a  substance  called 
caramel,  which  is  colored  more  or  less  brown.  When 
boiled  witli  dilute  acids,  cane-sugar  is  split  into  equal  parts 
of  dextrose  and  levulose.  The  mixture  of  the  two  is  called 
invert-sugar.  Yeast  gradually  transforms  cane-sugar  into 
dextrose  and  levulose,  and  these  then  undergo  fermenta- 
tion. CJanp.-anfrfl,r  floes  -not  fp.rpirnit. 

Sugar  of  Milk,  Lactose,  C12H22On  -f  Ha(X—  This  sugar 
occurs  in  the  milk  of  all  mammals.  It  is  obtained  in  the 


426  INTRODUCTION    TO   CHEMISTRY. 

manufacture  of  cheese.  Cow's  milk  consists  of  water, 
casein,  butter,  sugar  of  milk,  and  a  little  inorganic 
material,  in  about  the  following  proportions : 

Water 87    per  cent 

Casein 4 

Butter 3i 

Sugar  of  milk 4|       " 

Mineral  matter £       " 


100 

Cheese  is  made  by  adding  rennet  to  milk,  which  causes 
the  separation  of  the  casein.  The  sugar  of  milk  remains 
in  solution,  is  separated  by  evaporation,  and  purified  by 
recrystallization.  It  has  a  slightly  sweet  taste,  and  is 
much  less  soluble  in  water  than  cane-sugar. 

Souring  of  Milk. — Sugar  of  milk  ferments  under  certain 
circumstances,  and  is  transformed  mostly  into  lactic  acid. 
The  souring  of  milk  is  a  result  of  this  fermentation.  The 
lactic  acid  formed  coagulates  the  casein;  hence  the 
thickening. 

Cellulose,  C6H1005. — Cellulose  forms,  as  it  were,  the 
groundwork  of  all  vegetable  tissues.  It  presents  different 
appearances  and  different  properties,  according  to  the 
source  from  which  it  is  obtained;  but  these  differences  are 
due  to  substances  with  which  the  cellulose  is  mixed;  and 
when  they  are  removed,  the  cellulose  left  behind  is  the 
same  thing,  no  matter  what  its  source  may  have  been. 
The  'coarse  wood  of  trees  and  the  tender  shoots  of  the 
most  delicate  plants  consist  essentially  of  cellulose.  Cotton- 
wool, hemp,  and  flax  consist  almost  wholly  of  cellulose. 

Properties. — Cellulose  does  not  crystallize,  and  is  insolu- 
ble in  all  ordinary  solvents.  It  dissolves  in  concentrated 
sulphuric  acid.  If  the  solution  is  diluted  and  boiled,  the 
cellulose  is  converted  into  dextrin  and  dextrose.  It  will 


GUN-COTTON--P4PER-  S  TARCH.  427 

thus  be  seen  that  rags,  paper,  and  wood,  all  of  which  con- 
sist largely  of  cellulose,  might  be  used  for  the  preparation 
of  dextrose  or  glucose,  and  consequently  of  alcohol. 

Gun-cotton,  Pyroxylin,  Nitrocellulose.  —  Cellulose  has 
some  of  the  properties  of  alcohols ;  among  them  the  power 
to  form  ethereal  salts  with  acids.  Thus,  when  treated 
with  nitric  acid  it  forms  several  nitrates,  just  as  glycerin 
forms  the  nitrate  known  as  nitroglycerin  (which  see). 
The  nitrates  are  explosive,  and  are  used  for  blasting  under 
the  name  gun-cotton. 

Collodion. — A  solution  of  gun-cotton  in  a  mixture  of 
ether  and  alcohol  is  known  as  collodion  solution,  which  is 
much  used  in  photography.  When  poured  upon  any  sur- 
face, such  as  glass,  the  ether  and  alcohol  rapidly  evaporate, 
leaving  a  thin  coating  of  gun-cotton. 

Celluloid. — Celluloid  is  an  intimate  mixture  of  gun-cotton 
and  camphor.  As  it  is  plastic  at  a  slightly  elevated  tem- 
perature, it  can  easily  be  moulded  into  any  desired  shape. 
When  cooled  it  hardens. 

Paper. — Paper  in  its  many  forms  consists  mainly  of 
cellulose.  The  essential  features  in  the  manufacture  of 
paper  are,  first,  the  disintegration  of  the  substances  used. 
This  is  effected  partly  mechanically  and  partly  by  boiling 
with  caustic  soda.  Then  the  resulting  mass  is  converted 
into  pulp  by  means  of  knives  placed  on  rollers.  The  pulp, 
with  the  necessary  quantity  of  water,  is  then  passed 
between  rollers.  Rags  of  cotton  or  linen  are  chiefly  used 
in  the  manufacture  of  paper;  wood  and  straw  are  also  used. 

Starch.  C6H1005. — Starch  is  found  everywhere  in  the 
vegetable  kingdom  in  large  quantity,  particularly  in  all 
kinds  of  grain,  as  maize,  wheat,  etc. ;  in  tubers,  as  the 


42$  INTRODUCTION    TO   CHEMISTRY. 

potato,  arrowroot,  etc. ;  in  fruits,  as   chestnuts,  acorns, 
etc. 

Manufacture  of  Starch.— In  the  United  States  starch  is 
manufactured  mainly  from  maize ;  in  Europe,  from  pota- 
toes. The  processes  made  use  of  are  mostly  mechanical. 
The  maize  is  first  treated  with  warm  water;  the  softened 
grain  is  then  ground  between  stones,  a  stream  of  water 
running  constantly  into  the  mill.  The  thin  paste  which 
is  carried  away  is  brought  upon  sieves  of  silk  bolting-cloth, 
which  are  kept  in  constant  motion.  The  starch  passes 
through  with  the  water  as  a  milky  fluid.  This  is  allowed 
to  settle  when  the  water  is  drawn  off.  The  starch  is  next 
treated  with  water  containing  a  little  alkali,  the  object  of 
which  is  to  dissolve  gluten,  oil,  etc.  The  mixture  is  now 
brought  into  shallow,  long  wooden  runs,  where  the  starch 
is  deposited,  the  alkaline  water  running  off.  Finally,  the 
starch  is  washed  with  water,  and  dried  at  a  low  tempera- 
ture. 

Properties. — Starch  in  its  usual  condition  is  insoluble  in 
water.  If  ground  with  cold  water  it  is  partly  dissolved. 
If  heated  with  water  the  membranes  of  the  cells  of  which 
the  starch  is  composed  are  broken,  and  the  contents  form 
a  partial  solution.  On  cooling,  it  forms  a  transparent 
jelly  called  starch-paste.  By  dilute  acids  and  ferments 
starch  is  converted  into  dextrin,  maltose,  and  dextrose. 

Flour. — Wheat  flour,  which  may  serve  as  an  example  of 
flour  in  general,  contains  water,  starch  with  a  little  sugar 
and  gum,  gluten,  and  a  small  quantity  of  mineral  matter. 
The  finest  flour  contains  about  10  per  cent  of  gluten  and 
70  per  cent  of  starch.  Gluten  is  a  substance  that  resem- 
bles in  many  respects  the  white  of  eggs,  or  egg-albumin. 

Bread-making. — The  chemical  changes  which  take  place 
in  bread-making  are  of  special  interest.  Bread  is  made 


COMPOUNDS  FROM   COAL-TAR.  429 

by  mixing  the  flour  with  water  and  a  little  yeast .  The  dough 
thus  prepared  is  put  in  a  warm  place  for  a  time,  when  it 
rises.  The  rising  is  a  result  of  fermentation  caused  by  the 
yeast.  A  part  of  the  starch  contained  in  the  flour  is  con- 
verted into  sugar,  and  this  is  then  converted  into  alcohol 
and  carbon  dioxide  by  fermentation.  The  alcohol  passes 
off  for  the  most  part,  and  the  carbon  dioxide  in  striving 
to  escape  from  the  thick  gummy  dough  fills  the  mass  with 
bubbles  of  gas,  making  it  light  and  porous.  When  the 
loaf  is  put  into  the  oven  the  gases  contained  in  it  expand, 
making  it  still  lighter;  then  the  fermentation  is  checked 
by  the  heat  and  no  further  chemical  change  takes  place 
except  on  the  surface,  where  the  substances  are  partly 
decomposed  and  converted  into  a  dark-colored  product,  the 
crust. 

A    FEW    COMPOUNDS    FROM    COAL-TAR. 

Aromatic  Compounds. — The  fact  that  benzene,  C6H6, 
toluene,  C7H8 ,  and  other  hydrocarbons  are  obtained  from 
coal-tar  has  already  been  mentioned  (p.  404).  These 
hydrocarbons  are  the  starting-points  for  the  preparation 
of  a  very  large  number  of  compounds  of  carbon  which  are 
commonly  called  the  "aromatic  compounds,"  as  many  of 
them  have  a  pleasant  aromatic  odor. 

Nitrobenzene,  C6H5N02. — :This  substance  is  formed  by 
treating  benzene  with  nitric  acid : 

C.H.  +  HNO.  =  O.H.NO,  +  H.O. 

It  is  a  yellow  liquid  with  a  pleasant  odor  like  that  of  the 
oil  of  bitter  almonds.  It  is  much  used  under  the  name 
artificial  oil  of  bitter  almonds. 

Aniline.  CLILNIL. — When  nitrobenzene  is  treated  with 

y          D        5  2 

a  solution  from  which  hydrogen  is  given  off  the  oxygen  is 
extracted  and  replaced  by  hydrogen : 

C6H5N02  +6H  =  C6H5NH2  +  2H20. 


43°  INTRODUCTION    TO   CHEMISTRY. 

The  product  is  the  substance  known  as  aniline.  It  is  a 
colorless  liquid.  When  it  together  with  a  similar  sub- 
stance, known  as  toluidine,  is  treated  with  mercuric 
chloride,  Hg012  ,  or  arsenic  acid  it  is  converted  into  the  dye 
magenta,  which  is  the  substance  from  which  most  of  the 
aniline  dyes  are  prepared. 

Aniline  Dyes.  —  Of  these  a  large  number  are  known. 
They  are  all  derivatives  of  rosaniline,  of  which  magenta  is 
a  salt.  A  great  many  different  colors  of  aniline  dyes  are 
made,  some  of  them  of  great  beauty. 

Phenol,  Carbolic  Acid,  C6H60.  —  This  familiar  substance 
is  contained  in  coal-tar,  and  is  extracted  from  it  by  treat- 
ing with  caustic  soda  in  which  the  carbolic  acid  dissolves. 
When  pure  it  crystallizes  in  beautiful  colorless  rhombic 
needles.  It  has  a  peculiar,  penetrating  odor,  and  is 
poisonous.  It  is  much  used  as  a  disinfectant. 

Oil  of  Bitter  Almonds,  )  n  TT  n      m,  . 

Benzole  Aldehyde,         [  C,H60.-This  substai.ce  occurs 

in  combination  with  amygdalin,  which  is  found  in  bitter 
almonds,  laurel-leaves,  cherry-kernels,  etc.  Amygdalin 
belongs  to  the  class  of  compounds  known  as  glu  cos  i  ties, 
which  break  up  into  glucose  and  other  substances. 
Amygdalin  itself,  under  the  influence  of  emulsin,  which 
occurs  with  it  in  the  plants,  breaks  up  into  oil  of  bitter 
almonds,  hydrocyanic  acid,  and  dextrose  : 

C20H27NOn  +  2H20  =  C7H60  +  ONH  +  2C6H1206. 

Amygdalin.  Oil  of  Hydrocy-         Glucose. 


bitter  anic  acid. 

almonds. 


It  is  prepared  from  bitter  almonds,  which  yield  about 
1.5  to  2  per  cent.  It  is  a  liquid  which  has  a  pleasant 
odor. 


BALSAMS—  7V/AW/C  ACID.  431 

Benzole  Acid,  C7H602. — Benzole  acid  occurs  in  gum 
benzoin  and  in  the  balsams  of  Peru  and  Tolu,  and  is  made 
artificially  from  coal-tar  by  oxidizing  toluene,*  C7H8. 

Balsams  and  Odoriferous  Resins. — The  balsams  of  Peru 
and  Tolu  are  thick  fragrant  fluids  which  are  obtained  from 
certain  trees  in  South  America  and  elsewhere  by  cutting 
the  bark.  Benzoin  is  a  similar  substance.  These  as  well 
as  myrrh,  frankincense,  and  other  substances  of  the  kind 
are  used  for  their  odors.  The  odors  are  intensified  when 
the  substances  are  heated.  They  are  largely  used  as 
incense. 

Gallic  Acid,  C7H605. — Gallic  acid  occurs  in  sumach,  in 
Chinese  tea,  and  many  other  plants.  It  is  formed  by 
boiling  tannin  or  tannic  acid  with  sulphuric  acid.  It  is 
prepared  from  gall-nuts  by  fermentation  of  the  tannin 
contained  in  them.  It  is  closely  related  to  tannin  or 
tannic  acid. 

Tannic  Acid,  Tannin,  0UH1003, — This  substance  occurs 
in  gall-nuts,  from  which  it  is  extracted  in  large  quantities. 
It  is  soluble  in  water.  Its  solution  gives  a  dark  blue-black 
color  with  iron  salts.  Tannin  is  used  extensively  in  medi- 
cine, in  dyeing,  in  the  manufacture  of  leather  and  of  ink. 

EXPERIMENT  196.— Boil  10  grams  of  powdered  gall-nuts  with 
60  cc.  of  water,  adding  water  from  time  to  time.  A  solution  of 
tannin  is  thus  obtained.  Filter  after  standing.  In  a  test-tube 
add  to  some  of  this  solution  a  few  drops  of  a  solution  of  copperas 
(ferrous  sulphate).  A  colored  precipitate  is  formed  which  grad- 
ually changes  to  black. 

Tanning. — The  process  of  tanning  consists  in  treating 
hides,  from  which  the  hair  has  been  removed,  with  an  in- 
fusion of  hemlock  or  oak  bark,  or  of  sumach-leaves,  in 

*  The  name  toluene  comes  from  the  fact  that  this  hydrocarbon  was 
first  obtained  from  the  balsam  of  Tolu. 


43 2  INTRODUCTION   TO  CHEMISTRY. 

which  there  is  tannic  acid.  The  acid  combines  with 
certain  parts  of  the  hides,  forming  insoluble  compounds 
which  remain  in  the  pores,  converting  the  hides  into 
leather. 

Indigo. — In  several  plants  which  grow  in  the  East  and 
West  Indies,  in  South  America,  Egypt,  and  other  warm 
countries,  there  occurs  a  substance  called  indiran  which, 
when  treated  with  dilute  mineral  acids  or  certan  ferments, 
breaks  up  into  indigo-blue  and  a  substance  resembling 
glucose.  Commerical  indigo  contains  as  its  principal  in- 
gredient indigo-blue.  Indigo-blue  is  now  manufactured 
by  artificial  methods  on  the  large  scale. 

Naphthalene,  C10H8. — This  hydrocarbon  is  contained  in 
coal-tar  in  large  quantity.  It  is  a  beautiful  white  crystal- 
lized substance  much  used  in  the  preparation  of  dyes  and 
for  protecting  woollen  fabrics  from  moth. 

Anthracene,  CUH10. — Anthracene  like  naphthalene  is 
obtained  from  coal-tar.  Its  chief  use  is  in  the  preparation 
of  artificial  alizarin. 

Alizarin,  CUH804. — Alizarin  is  the  well-known  dye 
obtained  from  madder-root.  For  some  years  it  has  been 
made  artificially  from  anthracene,  and  the  cultivation  of 
madder  has  been  given  up.  Madder-root  was  used  for 
dyeing  "  Turkey-red."  Artificial  alizarin  is  exclusively 
used  for  this  purpose  at  present. 

Glucosides. — Glucosides  are  substances  that  occur  in 
nature  in  the  vegetable  kingdom.  They  break  down  under 
the  influence  of  ferments  and  dilute  acids  into  sugar  and 
other  compounds.  Amygdalin  has  already  been  mentioned. 
This  breaks  down  into  oil  of  bitter  almonds  and  dex- 
trose. Indican,  which  yields  indigo  and  dextrose,  is 
another  example. 


ALKALOIDS.  433 

Myronic  acid,  another  glucoside,  is  found  in  the  form 
of  the  potassium  salt  in  black  mustard-seed.  When  treated 
with  myrosin,  which  is  contained  in  the  aqueous  extract 
of  white  mustard-seed,  potassium  myronate  is  converted 
into  dextrose  and  oil  of  mustard. 

Alkaloids. — These  compounds  occur  in  plants,  and  are 
frequently  those  parts  of  the  plants  which  are  most  active 
when  taken  into  the  animal  body.  They  are  hence  some- 
times called  the  active  principles  of  plants.  Many  of  these 
substances  are  used  in  medicine.  They  all  contain  nitro- 
gen and  in  some  respects  resemble  ammonia.  Only  a  few 
of  the  more  important  alkaloids  need  be  mentioned  here. 

Quinine. — This  valuable  alkaloid  is  obtained  from  the 
outer  bark  of  certain  trees  which  grow  in  Peru.  The  bark 
is  known  as  Peruvian  bark. 

Cocaine  is  found  in  cocoa-leaves.  Its  hydrochloric-acid 
salt  has  recently  come  into  prominence  in  medicine,  owing 
to  the  fact  that  a  small  quantity  of  its  solution  placed  upon 
the  eye  or  the  gums  or  injected  beneath  the  skin  causes 
insensibility  to  pain. 

Nicotine  occurs  in  tobacco-leaves  in  combination  with 
malic  acid. 

Morphine  and  narcotine  are  the  principal  alkaloids 
found  in  opium,  which  is  the  evaporated  sap  that  flows 
from  incisions  in  the  capsules  of  the  white  poppy  before 
they  are  ripe. 


CHAPTER   XXXI. 
QUALITATIVE  ANALYSIS. 

General. — In  order  to  analyze  substances  chemists  make 
use  of  reactions  such  as  have  been  studied  in  the  earlier 
parts  of  this  book.  To  learn  to  analyze  complicated  sub- 
stances, long  practice  and  careful  study  of  a  great  many 
facts  are  necessary.  But  simple  substances  can  be  analyzed 
by  the  aid  of  such  facts  as  have  al  ready  been  studied.  It 
has  been  seen,  for  example,  that  certain  chlorides  are 
insoluble  in  water;  that  certain  sulphides  are  insoluble  in 
dilute  hydrochloric  acid;  and  that  other  sulphides  which 
are  soluble  in  dilute  hydrochloric  acid  are  insoluble  in 
neutral  or  alkaline  solutions.  Advantage  is  taken  of  these 
and  other  similar  facts  to  classify  substances  according  to 
their  reactions.  A  convenient  classification  for  purposes 
of  analysis  is  the  following :  •• 

GROUP  I.  Metals  whose  chlorides  are  insoluble  or  difficultly 
soluble  in  water.  This  group  includes:  Silvery  lead, 
and  mercury  (as  mercurous  salt). 

GROUP  II.  Metals  not  included  in  Group  I,  whose  sul- 
phides are,  however,  insoluble  in  dilute  hydrochloric 
or  nitric  acid.  This  group  includes:  Copper -,  mer- 
cury (as  mercuric  salt),  bismuth,  antimony,  arsenic, 
and  tin. 

GROUP  III.  Metals  not  included  in  Groups  I  and  II, 
whose  sulphides  are,  however,  precipitated  by  am- 
monium sulphide  and  ammonia.  This  group  in- 

434 


QUALITATIVE  ANALYSIS.  435 

eludes:   Aluminium,  chromium,   nicJcBl,  cobalt,   iron, 

zinc,  and  manganese. 
GROUP  IV.   Metals  not  included  in  Groups  I,  II,  and  III, 

but  which  are  precipitated  by  ammonium  carbonate, 

ammonia,    and    ammonium   chloride.      This    group 

includes:  Barium,  strontium,  and  calcium. 
GROUP  V.   Metals  not  included  in  Groups  I,  II,  III,  and 

IV,  but  which  are  precipitated  by  disodium  phosphate, 

HN"a2P04,  ammonia,  and  ammonium  chloride.     This 

group  includes:  Magnesium. 
GROUP  VI.  Metals  not  included  in  Groups  I,  II,  III,  IV, 

and  V.     This  group  includes:    Sodium,  potassium, 

and  ammonium. 

1.  Now,  suppose  you  have  a  substance  given  you  for 
analysis.     The  first  thing  to  do  is  to  get  the  substance  in 
solution^     See  whether  it  dissolves  in  water.     If  it  does 
not,  try  dilute  hydrochloric  acid.     If  it  does  not  dissolve 
in  hydrochloric  acid,  try  nitric  acid;  and  if  it  does  not 
dissolve  in  nitric  acid,  try  a  mixture  of  nitric  and  hydro- 
chloric  acids.     If  concentrated  acid  is  used,  evaporate  to 
dryiiess  011  a  water-bath  before  proceeding  further.     Then 
dissolve  m  water,   and  add  a  few  drops  of  hydrochloric 
acid.     K  a  precipitate  is  formed,  continue  to  add  the  acid 
drop  by  drop  until  a   precipitate  is  no  longer  formed. 
Filter  and  wash. 

What  may  this  precipitate  contain  ? 

2.  Pass  hydrogen  sulphide  through  the  filtrate  for  some 
time  and  let  stand.     Filter  and  wash. 

If  a  precipitate  is  formed,  what  may  it  contain  ? 

3.  Add  ammonia  and  ammonium  sulphide  to  the  filtrate. 
Filter  and  wash. 

If  a  precipitate  is  formed,  what  may  it  contain  ? 

4.  Add  ammonium  carbonate,  ammonia,  and  ammonium 
chloride  to  the  filtrate.     Filter  and  wash. 


4;>6  INTRODUCTION   TO   CHEMISTRY. 

If  a  precipitate  is  formed,  what  may  it  contain  ? 
5.  Add  disodium  phosphate,  ammonia,  and  ammonium 
chloride  to  the  filtrate.     Filter  and  wash. 

If  a  precipitate  is  formed,  what  may  it  contain  ? 
What  may  be  in  the  filtrate  ? 

Examples  for  Practice. — Before  attempting  anything  in 
the  way  of  systematic  analysis  it  will  be  well  to  experiment 
in  a  more  general  way,  with  the  object  of  determining 
which  one  of  a  given  list  of  substances  a  certain  specimen 
is. 

The  list  below  contains  the  names  of  the  principal  sub- 
stances with  which  you  have  thus  far  had  directly  to  deal 
in  your  work.  You  have  handled  them  and  have  seen 
how  they  act  toward  different  substances.  Suppose  now 
that  a  substance  is  given  you,  and  you  know  simply  that 
it  is  one  of  tho.se  named  in  the  list,  how  would  you  go  to 
work  to  find  out  which  one  it  is  ?  You  have  a  right  to 
judge  by  anything  in  the  appearance  or  in  the  conduct  of 
the  substance.  If  you  reach  a  conclusion,  see  whether 
you  are  right  by  further  experiments.  After  your  work  is 
finished  write  out  a  clear  account  of  what  you  have  done, 
and  state  your  reasons  for  the  conclusion  you  have  reached. 

For  example,  suppose  sodium  chloride  is  given  you. 
You  see  that  it  is  a  white  solid.  On  heating  it  in  a  small 
tube,  you  see  that  it  does  not  melt,  but  it  breaks  up  into 
smaller  pieces  with  a  crackling  sound.  It  is  soluble  in 
water.  Hydrochloric  acid  causes  no  change  when  added 
to  a  little  of  the  solid.  Is  it  a  carbonate  ?  Sulphuric  acid 
causes  evolution  of  a  gas.  Has  this  an  odor  ?  How  does 
it  appear  when  allowed  to  escape  into  the  air  ?  Is  it  nitric 
acid  ?  Collect  some  of  it  in  water.  How  does  this  solution 
act  on  a  solution  of  silver  nitrate  ?  By  this  time  you  have 
evidence  that  you  are  dealing  with  a  chloride,  but  you  do 
not  yet  know  which  chloride  it  is.  It  cannot  be  ammonium 


LIST  OF  SUBSTANCES  FOR  EXAMINATION.          437 

chloride.  Why?  It  may  be  either  potassium  or  sodium 
r-hloride.  Try  a  small  piece  in  the  flame.  What  color  ? 
You  now  have  good  reasons  for  believing  that  the  substance 
you  are  dealing  with  is  sodium  chloride.  To  convince 
yourself,  get  a  small  piece  of  sodium  chloride  from  the 
bottle  known  to  contain  it,  and  make  a  series  of  parallel 
experiments  with  this  and  see  whether  you  get  exactly  the 
same  results  that  you  got  with  the  specimen  you  were 
examining.  If  not,  account  for  the  differences. 

By  careful  work  there  will  be  no  serious  difficulty  in 
determining  which  one  of  the  substances  in  the  list  you  are 
dealing  with. 

List  of  Substances  for  Examination. 

1.  Sugar.  19.   Manganese  dioxide. 

2.  Mercuric  oxide.  20..  Charcoal. 

3.  Calc  spar.  21.  Calcium  sulphate  (Gyp- 

4.  Marble.  sum). 

5.  Copper.  22.  Copper  oxide. 

6.  Hydrochloric  acid.  23.  Ammonium  chloride. 

7.  Nitric  acid.  24.   Calcium    oxide    (Quick- 

8.  Sulphuric  acid.  lime). 

9.  Zinc.  25.   Sodium  nitrate. 

10.  Tin.  26.  Ammonium  nitrate. 

11.  Oxalic  acid.  27.  Sodium  chloride. 

12.  Sodium  carbonate.  28.  Potassium  bromide. 

13.  Ferrous  sulphate  (Cop-  29.  Potassium  iodide. 

peras).  30.   Iron  sulphide. 

14.  Roll-sulphur.  31.   Potassium  carbonate. 

15.  Iron-filings,  32.   Potassium  nitrate. 

16.  Carbon  bisulphide.  33.   Potassium  dichromate. 

17.  Lead.  34.  Red  lead  (Minium). 

18.  Potassium  chlorate.  35.   Lead  nitrate. 

[The  instructor  will,  of  course,  select  the  substance  and 
give  it  to  the  student  without  any  suggestion  as  to  what 


43 8  INTRODUCTION   TO   CHEMISTRY. 

it  is.  After  the  student  has  shown  that  he  can  tell  with 
certainty  which  substance  he  has,  some  simple  mixtures 
of  substances  selected  from  the  above  list  may  next  be 
given  for  examination.  Thus  charcoal  and  copper  oxide ; 
zinc  and  tin;  mercuric  oxide  and  iron-filings;  etc.,  etc.] 

STUDY  OF  GROUP  I. 

EXPERIMENT  197. — 1.  Prepare  dilute  solutions  of  silver  nitrate, 
AgNO3,  lead  nitrate,  Pb(NO3)2 ,  and  mercurous  nitrate,  HgNO3. 

2.  Add  to  a  small  quantity  of  each  separately  in  test-tubes  a 
little  hydrochloric  acid. 

What  is  formed  ? 

3.  Heat  each  tube  with  contents,  and  then  let  cool. 
What  difference  do  you  observe  ? 

4.  After  cooling,  add  a  little  ammonia  to  the  contents  of  each 
tube. 

What  takes  place  in  each  case  ? 

How  could  you  distinguish  between  silver,  lead,  and  mercury  ? 

5.  Mix  the  solutions  of  silver  nitrate,  lead  nitrate,  and  mer- 
curous nitrate,  and  add  a  little  of  the  mixture  to  considerable 
water  in  a  test-tube.    Add  hydrochloric  acid  as  long  as  it  causes 
the  formation  of  a  precipitate.    Heat  to  boiling.     Filter  rapidly 
and  wash  with  hot  water. 

What  is  iu  the  filtrate,  and  what  is  on  the  filter  ? 

6.  Let  the  filtrate  cool. 

What  evidence  have  you  that  there  is  anything  present  in  it  ? 

7.  Add  sulphuric  acid  to  a  little  of  the  liquid. 

8.  Add  hydrogen  sulphide  to  a  little  of  the  liquid. 

9.  Pour  ammonia  on  the  filter,  and  wash  out  with  water.   Then 
add  nitric  acid  to  the  filtrate. 

What  evidence  do  you  get  of  the  presence  of  silver  and  of 
mercury  ? 

STUDY  OF   GROUP  II. 

EXPERIMENT  198. — 1.  Prepare  dilute  solutions  of  copper  sul- 
phate, mercuric  chloride,  arsenic  trioxide  in  hydrochloric  acid, 
and  of  tin  in  hydrochloric  acid.  [Bismuth  and  antimony  are 
omitted,  as  their  presence  gives  rise  to  difficulties  hard  to  deal 


QUALITATIVE  ANALYSIS:   GROUP  II.  439 

with  intelligently  at  this  stage.]     Add  a  little  hydrochloric  acid 
to  the  solutions  of  copper  sulphate  and  of  mercuric  chloride. 

2.  Pass  hydrogen  sulphide  through  a  small  quantity  of  each  of 
the  solutions. 

What  takes  place  ?    What  are  the  substances  formed  ? 

3.  Filter  and  wash.     Treat  each  precipitate  with  a  solution  of 
yellow  ammonium  sulphide. 

What  takes  place  ?    Add  dilute  sulphuric  acid  to  the  nitrates. 
What  takes  place  ? 

4.  Treat   the  precipitates  obtained   from  the  copper  and  the 
mercury  salts  with  concentrated  warm  nitric  acid. 

Does  either  one  dissolve  easily?  What  is  the  color  of  the 
solution  ? 

5.  Treat  a  little  of  the  solution  obtained  in  4.  with  ammonia. 
"What  is  the  result  ?    How  can  you  detect  the  presence  of 

copper  ? 

6.  Treat  with  a  mixture  of  nitric  and  hydrochloric  acids  the 
precipitate  which  is  not  readily  dissolved  by  nitric  acid  alone. 
Evaporate  the  acid.     Add  water,  and  then  a  solution  of  tin  in 
hydrochloric  acid. 

What  is  formed  when  tin  is  dissolved  in  hydrochloric  acid  ? 

What  other  compound  of  tin  and  chlorine  is  there  ? 

[When  stannons  chloride,  SnCla ,  acts  upon  mercuric  chloride, 
HgCl<j ,  the  former  takes  a  part  or  all  of  the  chlorine  from  the 
latter,  forming  either  mercurous  chloride,  HgOl,  or  mercury, 
thus: 

SHgCl,  4-  SnCl2  =  SHgCl  +  SnCl«; 
HgCla  +  SnCl3  =  Hg        +  SnCl*.] 

7.  Treat  the  precipitate  obtained  in  the  case  of  the  arsenic  with 
4-5  cc.   of   a  concentrated    solution   of   ammonium   carbonate. 
To  the  solution  add   hydrochloric  acid  and   a   few   crystals   of! 
potassium  chlorate,  and  boil  until  chlorine  is  no  longer  given  off. 
Add  ammonia,  ammonium  chloride,  and  magnesium  sulphate  to 
the  solution.    [The  precipitate  is  ammonium  magnesium  arsenate, 
NH4MgAsO4.] 

8.  Dissolve  the  tin   precipitate    in   dilute   hydrochloric   acid. 
Add  a  few  small  pieces  of  zinc.     Dissolve  in  hydrochloric  acid 
the  tin  which  separates. 

What  will  the  solution  thus  obtained  contain  ? 


44°  INTRODUCTION   TO   CHEMISTRY. 

What  should  take  place  on  adding  the  solution  to  a  solution  of 
mercuric  chloride  ?    Try  it. 
Mix  the  solutions  prepared  in  1.,  and  proceed  as  follows  : 

9.  Pass  hydrogen  sulphide.     Filter ;  wash.     Treat  the  precipi- 
tate with  ammonium  sulphide.     Filter;  wash. 

What  is  now  in  solution  ? 
What  is  on  the  filter  ? 

10.  Treat    the   solution   with   dilute  sulphuric   acid.     Filter  ; 
wash.      Treat  the   precipitate  thus   obtained  with  concentrated 
ammonium  carbonate.      Filter;    wash.      Treat  the   solution    as 
directed  in  7.,  and  the  precipitate  as  in  8. 

11.  Treat  with  concentrated  warm  nitric  and  hydrochloric  acids 
the  precipitate  left  after  treating  with  ammonium  sulphide  as  in 
9.     Test  for  copper  as  in  5. ,  and  for  mercury  as  in  6. 

STUDY  OF  GROUP  III. 

ALUMINIUM. 

EXPERIMENT  199.— 1.  Prepare  a  solution  of  ordinary  alum. 
[What  is  ordinary  alum?] 

2.  Add  to   this  solution  ammonia,   ammonium  chloride,  and 
ammonium  sulphide.     Filter  and  wash.     Treat  the  precipitate 
with  hydrochloric  acid  ;  and  then  treat  the  solution  thus  obtained 
with  ammonium  chloride  and  ammonia. 

[Aluminium  does  not  form  a  sulphide ;  but  the  hydroxide, 
A1(OH)3,  is  formed  when  ammonia,  ammonium  chloride,  and 
ammonium  sulphide  are  added  to  a  solution  of  its  salts.  When 
the  hydroxide  is  treated  with  hydrochloric  acid  it  is  converted 
into  the  chloride,  A1C13 ,  which  dissolves  ;  and  when  the  solution 
of  the  chloride  is  treated  with  ammonia  the  hydroxide  is  precip- 
itated : 

AlOli  +  3NH3  +  3HaO  =  A1(OH)«  +  3NEUC1.] 

3.  Dissolve  the  precipitate  of  aluminium  hydroxide,  A1(OH)3 , 
in  as  little  hydrochloric  acid  as  possible,  and  add  a  cold  solution 
of  sodium  hydroxide.     Boil  the  solution  thus  obtained. 

4.  After  cooling  slowly  add  dilute  hydrochloric  acid.     When 
the  alkali  is  neutralized,  aluminium  hydroxide,  A1(OH)» ,  will  be 
precipitated.    It  will  dissolve  on  the  addition  of  more  acid  ;  and 
from  the  solution  thus  obtained  the  hydroxide  can  be  precipitated 
by  a  solution  of  ammonia. 


QUALITATIVE  ANALYSIS:   CHROMIUM -IRON.       44* 
CHROMIUM. 

EXPERIMENT  200. — 1.  To  5-10  cc.  of  a  solution  of  potassium 
dichromate  in  a  test-tube  add  10-15  drops  of  hydrochloric  acid 
and  10-15  drops  of  alcohol,  and  boil.  What  change  takes  place  ? 

[Under  the  conditions  the  chromium  is  changed  to  chromic 
chloride,  Or013 ,  and  the  potassium  to  potassium  chloride,  while 
some  of  the  oxygen  of  the  dichromate  acts  upon  the  alcohol,  con- 
verting it  into  aldehyde  : 

K9Cra07  +  8H01  =  2KC1  +  2CrCl3  +  4HaO  +  3O  ; 
3C2HflO  +  3O  =  30aH4O  +  3H2O.] 
Alcohol.  Aldehyde. 

2.  Treat  the  solution  of  chromic  chloride,  CrCU  ,  obtained  in  1. 
as  directed  in  2.  and  3.,  Experiment  199,  and  note  the  differ- 
ences. 

How  could  you  distinguish  between  aluminium  and  chromium  ? 

IRON. 

EXPERIMENT  201. — 1.  Prepare  a  solution  containing  ferrous 
chloride.  [See  Experiment  182.] 

2.  Convert  a  part  of  this  into  ferric  chloride.     [See  Experi- 
ment 182.] 

3.  Treat  each  of  these  solutions  with  ammonia  and  ammonium 
sulphide. 

[The  same  compound  of  iron  is  precipitated  in  both  cases,  and 
the  action  is  represented  thus  : 

FeCla  +  (NH4)2S  =  FeS  +  2NH4Cl ; 
2FeCl8  +  3(NH4)2S  =  2FeS  +  6NH4C1  +  S.] 

4.  Dissolve  the  precipitate  in  hydrochloric  acid  : 

FeS  +  2HC1  =  FeCla  +  H2S. 

5.  Convert  the  ferrous  into  ferric  chloride.    [See  Experiment 
182.] 

6.  Treat  with  ammonium  chloride  and  ammonia.     Filter  and 
wash.     Treat  the  precipitate  as  directed  under  3.,  Experiment 
199. 

What  differences  are  there  between  aluminium,  chromium,  and 
iron  ?  ^  «* 

7.  Filter  ;  dissolve  the  precipitate  in  hydrochloric  acid  ;  and 
treat  with  a  solution  of  potassium  ferrocyanide,  K4Fe(CN)e. 

The  precipitate  formed  in  this  case  is  Prussian  blue. 


442  INTRODUCTION   TO  CHEMISTRY. 

ZINC. 

EXPERIMENT  202.— 1.  Prepare  a  dilute  solution  of  zinc  sul- 
phate. 

2.  Treat  with  ammonia  and  ammonium  sulphide.    What  is  the 
color  of  the  precipitate  ?    The  composition  is  ZnS. 

3.  Dissolve  in  dilute  hydrochloric  acid  : 

ZnS  +  2HC1  =  ZnCl2  +  H2S. 

4.  Treat  with  ammonium  chloride  and  ammonia.     Is  a  pre- 
cipitate formed  ? 

5.  Add  enough  hydrochloric  acid  to  give  the  solution  an  acid 
reaction,  and  then  add  sodium  acetate,  NaC2H3O2 : 

ZnCl,  +  2NaC2H3O2  =  2NaCl  +  Zn(C3H,O9),. 

6.  Pass   hydrogen  sulphide  through  the  solution.     The  white 
precipitate  is  zinc  sulphide,  ZnS. 

What  differences  are  there  between  aluminium,  chromium, 
iron,  and  zinc?  How  could  they  be  separated  and  detected  if 
present  in  the  same  solution? 

[It  will  be  well  for  the  instructor  to  prepare  solutions  contain- 
ing two  or  more  members  of  Group  III,  and  to  give  them  to  the 
student  for  analysis.] 

MANGANESE. 

EXPERIMENT  203.— 1.  Treat  a  little  manganese  dioxide  in  a 
test-tube  with  hydrochloric  acid.    Boil,  dilute,  and  filter. 
What  have  you  in  solution  ?     [See  page  102.] 

2.  Treat  as  under  2.,  3.,  4.,  5.,  6.,  in  the  preceding  Experiment. 
In  what  respects  do  manganese  and  zinc  differ? 

3.  To  the  solution  through  which  you  have  just  passed  hydro- 
gen sulphide  add   sodium  hydroxide,  NaOH,  until  most  of  the 
acetic  acid  is  neutralized  ;  heat  gently  and  add  bromine-water. 
Let  the  liquid  stand  for  an  hour. 

What  takes  place  ?  [The  composition  of  the  precipitate  is 
represented  by  the  formula  Mn(OH)4.] 

How  could  you  separate  manganese  from  the  other  members 
of  the  group  ? 

EXPERIMENT  204.  — 1.  Mix  dilute  solutions  of  alum,  chromic 
chloride  (prepared  as  in  Experiment  200,  1.),  ferrous  chloride 


QUALITATIVE  ANALYSIS:  MANGANESE— CALCIUM.  443 

(prepared  as  in  Experiment  182),  zinc  sulphate,  and  manganous 
chloride. 

2.  Treat  with  ammonia,  ammonium  chloride,  and  ammonium 
sulphide.     Filter  and  wash. 

3.  Treat  the  precipitate  with  dilute  hydrochloric  acid  ;   treat 
with  nitric  acid  to  convert  ferrous  chloride  into  ferric  chloride 
(Experiment  182)  ;   and  then   treat   the  solution  thus  obtained 
with  ammonium  chloride  and  ammonia. 

What  have  you  in  the  precipitate  ?    (Call  this  A.) 
What  in  the  solution  ?    (Call  this  B.) 

4.  Dissolve  the  precipitate  in  a  little  dilute  hydrochloric  acid, 
and  add  a  cold  solution  of  sodium  hydroxide,  more  than  enough 
to  neutralize  the  hydrochloric  acid.     Filter  ;  dissolve  the  precipi- 
tate in  hydrochloric  acid  ;  and  treat  with  a  solution  of  potassium 
ferrocyanide,    K4Fe(CN)6.     [See  Experiment  201,  7.]    Boil  the 
nitrate  from  the  precipitate  of  ferric  hydroxide.     What  is  pre- 
cipitated ?    Treat  the  nitrate  as  directed  in  Experiment  197,  4. 

5.  Treat  the  solution  B  (see  under  3.,  above)  as  directed  under 
5.  and  6.,  Experiment  202  ;   and  under  3.,  Experiment  203.     Ex- 
amine mixtures  containing  members  of  Group  III. 

STUDY  OF  GKOUP  IV. 

CALCIUM. 

EXPERIMENT  205.— 1.  Prepare  a  solution  of  calcium  chloride  by 
dissolving  a  little  calcium  carbonate  (marble)  in  hydrochloric 
acid.  What  is  the  reaction  ? 

2.  Treat  with  ammonium  chloride,  ammonia,  and  ammonium 
carbonate,  (NHOsCOs.     Filter  and  wash. 

What  takes  place  ?     Write  the  reaction. 

3.  Treat  with  potassium  chromate.     Is  a  precipitate  formed? 

4.  Dissolve  the  precipitate  in  dilute  hydrochloric  acid.     Treat 
a  small  part  of  this  solution  with  a  solution  of  calcium  sulphate 
in  water.     Treat  another  small  part  with  ammonia  and  ammo- 
nium oxalate,  (NII4)aC2O4.     The  precipitate  is  calcium  oxalate, 
CaC3O4.     Does  a  solution  of  calcium  chloride  give  a  precipitate 
when  treated  with  a  solution  of  calcium  sulphate  ? 


444  INTRODUCTION  TO  CHEMISTRY. 

BARIUM. 

EXPERIMENT  206. — 1.  Prepare  a  dilute  solution  of  barium  chlo- 
ride in  water. 

2.  Treat  as  directed  under  2.,  preceding  experiment. 

3.  Dissolve  the  precipitate  in  dilute  hydrochloric  acid.     Treat 
a  small  part  of  this  solution  with  a  solution  of  calcium  sulphate 
in  water.     Treat  another  portion  with  ammonia  and  ammonium 
oxalate.     The  precipitate  is  barium  oxalate. 

4.  Treat  a  portion  of  the  barium  chloride  solution  with  potas- 
sium chromate.     The  yellow  precipitate  is  barium  chromate. 

What  differences  do  you  notice  between  the  conduct  of  calcium 
and  that  of  barium  ? 

In  order  to  detect  calcium  in  the  presence  of  barium,  precipitate 
the  barium  as  chromate  and  test  the  filtrate  for  calcium  by  the 
ammonium  carbonate  test. 

Mix  the  solutions  of  barium  and  calcium  chlorides,  and  try  the 
reactions  described  in  Experiments  205  and  206. 

STUDY  OP  GROUP  V. 

MAGNESIUM. 

EXPERIMENT  207.— 1.  Prepare  a  dilute  solution  of  magnesium 
sulphate  in  water. 

2.  Add  ammonium  chloride,  ammonia,  and  ammonium  carbon- 
ate.   Is  a  precipitate  formed  ?    Compare  this  reaction  with  that 
obtained  in  case  of  calcium  and  barium  chlorides. 

3.  Add  ammonium  chloride,  ammonia,  and  disodium  phosphate. 
The  precipitate  is  ammonium  magnesium  phosphate,  NH4MgPO4. 

What  similar  precipitate  has  already  been  obtained  ?  (See 
Experiment  198,  7.) 

4.  Mix  solutions  of  barium,  calcium,  and  magnesium  chlorides, 
and  see  whether  you  can  detect  the  three  metals  by  means  of  the 
reactions  described  in  Experiments  205,  206,  and  207.     It  is  nec- 
essary to  remove  calcium  and  barium  before  testing  for  mag- 
nesium. 


QUALITATIVE  ANALYSIS:   GENERAL   DIRECTIONS.   445 


STUDY   OF   GROUP  VI. 

EXPERIMENT  208. — 1.  Potassium  can  be  detected  by  means  of 
the  color  it  gives  to  a  flame  (see  Experiment  151) ;  and  also  by  the 
fact  that  when  chlorplatiuic  acid,  HaPtCl6 ,  is  added  to  a  solution 
of  a  potassium  salt,  the  salt,  K2PtO!« ,  is  precipitated.  Try  this. 

2.  Sodium  is  detected  by  means  of  the  flame  reaction  (see  Ex- 
periment 151). 

3.  Ammonium  salts  are  detected   by  adding  an  alkali,  when 
ammonia  gas  is  given  off,  and  this  is  easily  recognized. 

General  Directions. — By  the  aid  of  the  reactions  thus  far 
studied  it  will  be  found  possible  to  analyze  substances  con- 
taining the  following  metals  either  alone  or  mixed  together : 
Silver,  lead,  mercury,  copper,  tin,  arsenic,  aluminium, 
chromium,  iron,  zinc,  manganese,  calcium,  barium,  mag- 
nesium, potassium,  sodium,  and  ammonium.  After  the 
metals  have  been  detected,  the  next  question  to  be 
answered  is:  In  what  forms  of  combination  were  they 
present  in  the  original  substance  taken  for  analysis  ?  Or, 
in  other  words,  what  salts  were  present  ?  To  answer  this 
question,  recall  the  experiments  you  have  made  in  the 
general  reactions  of  chlorides,  nitrates,  sulphates,  and  car- 
bonates. These  are  the  most  common  salts  and,  for  the 
present,  it  will  be  best  to  confine  your  work  to  these. 

Classification  of  Substances  Studied. — It  will  now  be 
well  to  draw  up  a  table  containing  the  names  and  symbols 
of  all  the  substances  with  which  you  have  had  to  deal, 
classifying  them  into : 

(1)  Elements  and  Compounds  ; 

(2)  Acids,  Bases,  and  Salts. 

Under  Elements  state  the  principal  source  and  the  prin- 
cipal method  of  getting  each. 

Under  Compounds  state  the  source  and  the  principal 
method  of  preparation  of  each, 


44 6  INTRODUCTION   TO  CHEMISTRY. 

Classify  all  the  compounds  you  have  had  to  deal  with 
iiito: 

(1)  Those  which  are  gaseous; 

(2)  Those  which  are  liquid ; 

(3)  Those  which  are  solid  at  the  ordinary  temperature ; 

(4)  Those  solids  and  liquids  which  easily  undergo  change 
when   heated    (state   what   the   change   is,  and   give   the 
equation  expressing  the  change). 

Classify  the  compounds  further  into : 

(1)  Those  which  are  soluble  in  water; 

(2)  Those  which  are  insoluble  in  water. 


APPARATUS  AND  CHEMICALS. 

A  FEW  of  the  experiments  described  in  this  book  are 
not  suitable  for  general  laboratory  practice :  they  are  in- 
tended for  the  lecture-room  and  require  a  trained  experi- 
menter to  secure  the  best  results.  Others  again,  although 
easily  performed  by  any  student,  yet  on  account  of  the 
character  of  the  apparatus  required — its  cost  or  its  bulki- 
ness — may  have  to  be  omitted  from  the  laboratory  course 
after  they  have  been  performed  in  the  lecture-room.  To 
these  two  classes  the  following  may  be  considered  as 
belonging:  Nos.  4,  25,  26,  27  (with  reference  to  potas- 
sium), 28,  34,  43,  45,  47,  48,  55. 

As  regards  the  -apparatus  called  for,  the  following  may 
be  said :  To  secure  the  best  results  the  form  described  had 
best  be  closely  followed.  Changes  will  sometimes  be 
•advisable  to  meet  special  conditions.  For  example,  on 
account  of  the  difficulty  of  obtaining  large  corks  free  from 
perforations  and  therefore  suitable  for  wash-cylinders,  an 
excellent  substitute  will  be  found  in  a  wide  Il-tube,  in 
which  the  wash-liquid — sulphuric  acid,  water,  potassium 
permanganate  solution,  etc. — acts  as  a  "trap,"  merely 
closing  the  bend.  When  the  quantity  of  gas  to  be  purified 
is  not  great,  this  device  gives  excellent  results. 

Again,  if  it  is  necessary  still  further  to  reduce  the  cost 
of  the  apparatus  to  be  used,  passable  results  can  be 
obtained  by  the  use  of  wide  test-tubes,  in  the  place  of 

447 


44 8  APPARATUS  AND   CHEMICALS. 

flasks,  in  such  experiments  as  Nos.  15,  49,  70,  92,  93,  94, 
05,  113,  114.  Of  course  the  quantities  of  materials  used 
would  in  such  case  be  greatly  decreased. 

As  a  rule,  it  is  better,  whenever  a  solid  substance  is  to 
be  heated  to  a  high  temperature,  to  use  a  tube  of  hard 
glass.  An  ordinary  arsenic-tube,  or  mat-trass,  serves  very 
well. 

For  the  benefit  of  those  who  have  no  laboratory  at  com- 
mand, and  who  may  wish  to  make  arrangements  for  going 
through  with  the  experimental  work,  the  following  lists 
have  been  drawn  up.  In  them  are  included  everything 
necessary  to  perform  the  experiments  on  a  small  scale. 
Should  it  be  desired  to  fit  up  a  room  with  conveniences 
for  students,  the  amount  of  apparatus  necessary  would 
depend  upon  the  number  of  students,  but  for  each  indi- 
vidual the  expense  would  be  small,  as  many  of  the  pieces 
of  apparatus,  such  as  are  included  in  List  II,  need  not  be 
multiplied.  In  place  of  some  of  the  pieces  of  apparatus 
described  in  the  book,  ordinary  kitchen  utensils  will 
answer :  thus,  for  example,  instead  of  the  trough  for  col- 
lecting gases,  a  tin  pan  or  a  deep  earthenware  dish  may  be 
used;  instead  of  the  water-bath,  a  stew-pan,  fitted  with 
two  or  three  different-sized  tin  or  sheet-iron  rings;  and  in 
the  place  of  glass  cylinders  for  working  with  gases,  wide- 
rnouthed  cheap  bottles. 

With  regard  to  the  chemicals  the  same  thing  may  be 
said :  Some  of  those  on  the  list  are  provided  for  in  quantity 
sufficient  for  several  students.  -The  amounts  in  such 
cases  are  as  small  as  can  generally  be  obtained  from 
dealers. 

To  summarize:  List  I  comprises  such  apparatus  as  will 
probably  be  needed  for  each  student ;  List  II,  such  appa- 
ratus as  will  serve  without  duplication  for  a  small  class ; 
List  III,  the  chemicals  actually  needed  for  each  student, 
as  nearly  as  can  be  calculated  under  the  circumstances. 


APPARATUS  AND   CHEMICALS. 


449 


LIST  I. — APPARATUS. 


Arsenic-tubes,  6 $0  30 

Beakers,  nest  (100-700  cc.) 90 

Blowpipe 14 

Bunsen  Burner „ 45 

Combustion-tubing:,  1  ft 18 

Corks,  2  dozen,  assorted  25 

Crucibles.porcelain,  2  (35-40  mm.)  37 

Deflagrating-spoon 25 

Evaporating  -  dishes,  2  (75-100 

mm.)  48 

File,  round 20 

".triangular  20 

Filter-paper,  1  quire  35 

Flasks,  Florence,  4  (1,  50-100  cc.; 

1,250:  1.  500;  1.750)  71 

Flasks,  Wolff,  1  (300  cc.) 45 

Funnels  2  (1,  50  mm.;  1,  90  mm.)  30 

Gauze,  wire,  6  X  6  in 10 

Glass  tubing,  soft,  &  Ib 15 

"  rod,loz ...  10 


Iron  pan  (5  in.)  $0  20 

"    stand,  with  clamp 90 

Mortar,  porcelain  (100  mm.) 50 

Retorts,  3  (1,  60  cc.;  1,  100;  1,  250, 

tubulated) 75 

Rubber  tubing.  3ft.  for  burner..  39 

"      ,2  ft.  for  connec- 
tions    20 

Safety-tube 20 

Test-tubes,   12  (6,  6x^6  in.;    6, 

6x%in.) 35 

Test-tube  Stand.. 25 

Thistle-tube.  — 12 

Tripod 30 

U  tubes,  2  (4  X  ^  in.)  28 

Watch-glasses,  2  (50  mm.) 10 

Wire :    1  ft.  magnesium  ;    6  in. 

platinum 35 

$10  77 


LIST  II. 


Burette,  Mohr,  graduated  to  •£, 

cc.,  50  cc.  complete  (20  p.  c.)..$l  50 
Cells,  Bunsen,  2  Quarts  (10  p.  c.).   2  20 

Cork-borers,  set  (6) 1  00 

Condenser  and  tubing  (20  p.  c.)..   1  85 
Gas-measuring  tube,  graduated 

to  Jcc..  25  cc.  (20  p.  c.) 100 

Magnet,  6-in.  horseshoe 40 


Measuring-glass,  4  oz.  (10  p.  c.).  .$0  30 
Pinch-cock,    Hoffman,    medium 

(20  p.  c.)  ...     25 

Scales,  set  (20  p.  c.) 85 

Weights,  set  (20  p.  c. ) 75 

$10  10 


LIST  III. — CHEMICALS. 


Acid.  Hydrochloric  (cone.)  ^  Ib. 

(bottle  12  cents  extra) $0  10 

Acid,  Nitric  (cone.),  \&  Ib.  \bottle 

12  cents  extra) 10 

Acid,  Oxalic,  1  oz    10 

"      Sulphuric     (cone.),    2   Ibs. 

(bottle  15  cents  extra) 10 

Alcohol,  8  oz.  (bottle  8  cents  ex- 
tra)   20 

Alum,  2oz1 10 

Ammonia  (cone.),  %  Ib.  (bottle  12 

cents  extra) 10 

Ammonium  Carbonate,  2  oz.  (bot- 
tle 4  cents  extra) ..  10 

Chloride,  «4  Ib 10 

"          Nitrate,  1  oz  10 

Antimony,  1  oz 10 

Arsenic  Trioxide,  2  ox ,...  10 

Barium  Chloride,  2  oz 10 

Bismuth,  Y±  oz 10 

Bone-black,  1  oz. .  10 

Borax,  1  oz  10 

Calcium  Chloride,  ^  Ib.  (bottle  8 

cents  extra)  10 

"       Fluoride,  1  oz 10 

Carbon  Bisulphide,  4  oz.  (bottle  4 

cents  extra)  10 

Copper  shavings,  ^  Ib 20 


Copper  Oxide,  2  oz $0  10 

Sulphate,  ^  Ib ...  10 

Ferric  Chloride,  1  oz 10 

Ferrous  Sulphate,  2  oz  10 

'*      Sulphide,  ^lb 10 

Gall-nuts,  1  oz  10 

Glucose,  5  oz  ..     ... 10 

Gypsum  (crystallized),  14  Ib 10 

lod  i  n  e ,  V6  oz .  (bottle  5  ce  n  ts  extra)  1 5 

Iron  Filings,  2  oz 10 

Lead  (granulated),  2  oz 10 

"     Nitrate,  2  oz 10 

"     Oxide,  1  oz  10 

"     Peroxide,  1  oz 10 

Litmus,  1  oz 10 

"       Paper,    red   and  blue,   1 

sheet  each    10 

Magnesium  Sulphate,  1  oz 10 

Manganese  Dioxide,  yz  Ib 10 

Mercuric  Oxide,  1  oz    15 

Mercury,    2   oz.  (bottle    3  cents 

extra) 10 

Minium,  1  oz 10 

Phosphorus,  1  oz.  (bottle  5  cents 

extra)     15 

Potassium  Bromide,  1  oz  10 

Carbonate.  J4  Ib 10 

Chlorate,  %  Ib .  10 


45°  APPARATUS  AND   CHEMICALS. 


Potassium  Chromate,  2  oz    $010 
"          Bichromate,  }4  Ib  10 
Ferrocjanide,  1  oz.  .  .         10 
"         Hydroxide,  6  oz.  (bot- 

Sodium, Hydroxide.  J4  Ib.  (bottle 
5  cents  extra)  ..   .  $0  15 
"        Nitrate,  2  oz        10 
"        Phosphate,  2  oz.     .               10 

tle  6  cents  extra).       20 
"         Iodide,  1  oz    (bottle  3 

Sulphate,  J4  Ib  10 
Strontium  Nitrate,  1  oz  10 

cents  extra)  ...   .         25 

Sulphur,  roll   \$  Ib  10 

Nitrate,  2  oz  10 
"         Permanganate,  2  oz.         10 
Sodium,  1  dram  (bottle  4  cents 
exira)                          10 

Tartar  Emetic,  1  oz    10 
Tin.  granulated,  14  Ib  10 
Zinc,          "            1  Ib   20 
"    Sulphate  1  oz                              10 

"        Carbonate,  2  oz  10 
Chloride,  1  Ib  10 

$725 

The  publishers  do  not  deal  in  apparatus  and  chemicals, 
nor,  they  may  as  well  say,  receive  commissions  on  them. 
Any  orders  should  be  sent  direct  to  the  dealers. 

Messrs.  Eimer  &  Amend,  Nos.  205  to  211  Third 
Avenue,  New  York,  whom-  the  publishers  take  the 
responsibility  of  recommending  as  thoroughly  reliable, 
will  furnish  each  of  the  above  articles  at  the  price  given. 

If  several  pieces  of  the  apparatus  in  List  I  are  taken,  a 
discount  of  10  per  cent  will  be  made;  on  a  complete  set, 
20  per  cent  discount  will  be  allowed;  on  three  or  more 
sets,  25  per  cent. 

One  or  more  of  the  articles  in  List  II,  if  not  marked 
"  20  per  cent,"  will  be  supplied  at  25  per  cent  discount  if 
ordered  with  sets  of  the  apparatus  in  List  I. 

A  discount  of  10  per  cent  will  be  given  on  a  complete 
set  of  the  chemicals  (List  III),  and  of  15  per  cent  on  three 
or  more  sets. 

For  most  items  less  than  the  whole  set  there  will  have 
to  be  a  small  additional  charge  for  packing.  It  should  be 
realized,  however,  that  usually  the  charge  for  packing  one 
article  must  be  as  large  as  for  several.  Some  articles  can, 
of  course,  be  mailed  without  any  charge  for  packing. 


INDEX. 


Acetates,  414 
Acetylene,  407,  409 
Acid,  acetic,  404,  414 

arsenic,  266 

arsenious,  267 

benzoic,  431 

boric,  271 

broinic,  232 

butyric,  415 

carbolic,  430 

carbonic,  187 

chlorauric,  401 

chloric,  116,  120 

chlorous,  120 

chlorplatinic,  318,  399 

chromic,  393 

citric,  418 

dithionic,  255 

ferric,  388 

formic,  414 

gallic,  431 

hydriodic,  234 

hydrobroinic,  231 

hydrochloric,  42,  101, 102,  108, 
108,  109 

hydrocyanic,  201 

hydrofluoric,  235 

hypobromous,  232 

hypochlorous,  117 

hyposulphurous,  255 

iodic,  235 

lactic,  417 

malic,  417 

metaboric,  272 

metaphosphoric,  263 

metarsenic,  267 

metastannic,  377 

myronic,  433 


Acid,  nitric,  15,  42,  144,  153 

nitrosyl-sulphuric,  252 

nitrous,  144,  159 

oleic,  419 

orthophosphoric,  262 

oxalic,  189,  417 

palmitic,  415 

perchloric,  120 

phosphoric,  262 

phosphorous,  264 

propionic,  415 

prussic,  202 

pyroarsenic,  267 

pyrogallic,  357 

pyropbosphoric,  263 

pyrosulphuric,  256 

salts,  255 

seleuic,  256 

silicic,  275 

stannic,  376 

stearic,  415 

sulphuric,    15,    42,    103,    109. 
139,  251 

sulphurous,  249 

tannic,  431 

tartaric,  417 

telluric,  256 

tetraboric,  272 

tetrathionic,  255 

thiosulphuric.  255 

trithionic,  255 
Acid-forming  elements,  220 
Acids,  42,  96,  97,  121,  123,  127, 
220 

dibasic,  254 

fatty,  415 

monobasic,  254 

organic,  422 


452 


INDEX. 


Acids,  tribasic,  263 
Agate,  276 
Air,  135,  141,  230 
Alabaster,  829 
Albumin,  168,  403 
Alcohol,  ethyl,  404,  410 

methyl,  404,  410 
Alcohols,  421 
Aldehyde,  413 

benzole,  430 
Alizarin,  432 
Alkalies.  121,  302 
Alkaloids,  433 
Allylene,  407 
Alum,  ordinary,  365 
Aluminates,  363 
Aluminium,  361 

alloys,  363 

compounds,  363,  368,  440 

group,  361 

hydroxide,  363 

oxide,  363 

silicates,  365 

sulphate,  363 
Alums,  365 

Amalgamation-process,  355 
Amalgams,  352 
Amethyst,  276 
Ammonia,  144,  145,  151,  158 

composition,  149 

formation,  143 

water,  174 
Ammonium,  148 

chloride,   144,  316 

chlorplatinate,  398 

compounds,  445 

hydrosulphide,  318 

hydroxide,  147 

nitrate,  161 

salts,  148,  315 

sodium  phosphate,  318 

sulphide,  316 
Amygdalin,  430 
Anaesthetics,  409,  418 
Analysis,  51,  246,  291,  434 

of  water,  52 
Anhydride,  boric,  272 

carbonic,  181 

nitric,  160 

nitrous,  160 

permanganic,  390 


Anhydride,  silicic,  276 
Anhydrides,  160 
Anhydrite,  329 
Aniline,  429 

dyes,  430 

Anthracene,  404,  432 
Anthracite  coal,  173 
Antimony,  104,  267 

acids  of,  267 

salts  of  268 

trichloride,  104 
Apatite,  258,  262,  381 
Aqua  regia,  159 
Aragonite,  327 
Argon,  141,  236 
Aromatic  compounds,  429 
Arsenic,  264 

acids  of.  266 

compounds,  488 

trioxide,  266,  267 

white,  178 
Arsine,  264 
Asbestos,  839 
Ash,  black,  313 
Atomj£  theory,  81 

weights,  83,  226 

determination  of,  85,  206,  358 
Atoms,  81 
Avogadro's  hypothesis,  205 

Balloons,  46 
Balsams,  431 
Barium,  837 

compounds,  444 

dioxide,  71,  99,  337 

hydroxide,  337 

oxide,  337 

sulphate,  294 

Baryta. water,  137,  138,  176,  337 
Base-forming  elements,  226 
Bases,  121,  123,  127,  226,  278 
Bauxite,  361 
Bell-metal,  348 
Benzene,  404,  407,  429 
Benzine,  406 
Benzoin,  431 

Beryllium  (=  glucinum),  322 
Bessemer  steel,  382 
Bismuth,  268 

salts  of,  269 
Bituminous  coal,  173 


INDEX. 


453 


Blast-furnace,  379 
Bleaching,  105,  106,  249 

powder,  117,  119,  325 
Blowpipe,  191 
Boiling-point  method,  214 
Bone-black,  172 
Bone-oil,  404 
Boracite,  271 
Borax,  27,  315 
Boric  acid,  271 

anhydride,  272 
Boron,  271 

chloride,  271 

crystallized,  271 
Boyle's  law,  57 
Brass,  343,  348 
Bread-making,  428 
Breathing,  35 
Bricks,  368 
Britannia  metal,  375 
Bromides,  230 
Bromine,  229 
Bronze,  348 
Bunsen  burner,  200 
Burning  in  the  air,  32 
Butane,  406 
Butter,  419 
Butylene,  407 

Cadmium,  339 
Caesium,  319 
Calcite,  327 
Calcium,  322 
Carbide,  202,  322 

carbonate,  327 

chloride,  51, 114,  137,  139, 145 
323 

compounds,  322,  443 

hydroxide,  323 

hypochlorite,  325 

group,  322 

oxide,  323 

phosphates,  331 

silicates,  333 

sulphate,  329 

sulphide,  336 
Calomel,  352 

Cane-sugar,  423,  424.  425 
Caramel,  425 
Carbides,  202 
Carbohydrates,  423 


Carbon,  27,93,96,  167,  174 

bisulphide,  242,  256 

dioxide,  179 

cycle  of,  in  nature,  185 
in  the  air,  138,  141 
Carbon  group,  274,  277 

monoxide,  188 

silicide,  275 

Carbonates,  181,  187,  296 
Carborundum,  275 
Carnallite,  339 
Carnelian,  276 
Casein,  426 
Cassiterite,  374 
Cast-iron,  381 
Caustic  potash,  40,  303 

soda,  40,  138,  310 
Celluloid,  427 
Cellulose,  170,  403,  42« 
Cementation,  382 
Cements,  336 
Cerium,  277 
Cerussite,  373 
Chalcocite,  346 
Chalk,  327 
Charcoal,  170 

animal,  172 

filters,  172 

reduction  by,  178 

wood,  171,  172 
Chemical  action,  13,  17 

changes,  2 

energy,  37 

work,  37 
Chemistry,  3 
Chloral,  413 

hydrate,  413 
Chlorates,  294 
Chlorides,  107,  284,  286 
Chlorine,  101,  105,  229 

acids,  120 

bleaching  by,  105 

comparison  with  fluorine,  bro- 
mine, and  iodine,  229 

hydrate,  106 

oxides  of,  120 
Chloroform,  409 
Chromates,  393,  394 
Chrome  alum,  395 

yellow,  1373,  895 
Chromic  acid,  393 


454 


INDEX. 


Chromic  chloride,  395,  441 

iron,  393 
Chromium,  393 

compounds,  393,  441 
Cinnabar,  351 
Clay,  361,  365 
Coal,  173,  404 
Coal-gas,  191 
Coal-tar,  174,  404,  429 
Cobalt.  389 
Cocaine,  433 
Coke,  171 

Collection  of  gases,  8 
Collodion,  427 
Colurnbiuin,  269 
Combination,  laws  of  chemical, 

75,  77 

Combining- weights,  29,  31 
Combustion,  33,  180 
Compounds,  chemical,  12 
Conservation  of  energy,  75,  186 
Copper,  15,  104,  163,  346 

acetate,  414 

alloys,  348 

compounds,  349,  438 

group,  346 

oxide,  98,  177,  350 

pyrites,  346 

sulphate,  102,  350 

sulphide.  351 
Copper-plating,  351 
Copperas,  387 
Corrosive  sublimate,  353 
Corundum,  363 
Cryolite,  235,  309,  361 
Crystallography,  240 
Cupric  compounds,  349 
Cuprous  compounds,  349 

oxide,  350 
Cyanogen,  201 

Dalton  and  Gay  Lussac's  law,  56 
Deacon's  Process,  102 
De«omposition,  double,  99 

heat  of,  37 
Decrepitation,  310 
Definite  proportions,  law  of,  75 
Deliquescence,  51 
"  Developers,"  357 
Dextrin,  423 
Dextrose,  423,  424,  430 


Diamond,  168 
Dissociation,  126,  210 
Distillation,  67 
Dolomite,  179,  339 
Double  decomposition,  99 
Dulong  and  Petit's  Law,  360 
Dynamite,  420 

Earthenware,  368 
Efflorescence,  50 
Electric  currents,  6 
Electrodes,  8 
Electrolysis,  8 
Electrolytes,  126,  214 
Electrolytic  dissociation,  126,  214 
Electrotype,  351 

Elements,   10,  18,  19,  208,   216, 
221,  226,  227 

base-forming,  278 

list  of,  20 

molecules  of,  208 

names  of,  19 

natural  families  of,  221 

specific  heat  of,  358 

substituting  power  of,  216 
Emery,  363 
Emu  lain,  430 
Epsom  salt,  340 
Erbium,  20 
Essences,  420 
Etching,  236 
Ethane,  406 
Ether,  418 
Ethereal  salts,  418 
Ethers,  418 
Ethyl  alcohol,  410 

butyrate,  420 

nitrate,  419 
Ethylene.  407.  409 
Eudiometer,  55 

Explosion  of  hydrogen  and  oxy- 
gen, 54,  62* 

Fats,  419 

Feldspar,  302,  361,  365,  366 
Fermentation.  180,  404,  410,  411 
Ferric  acid,  388 

chloride,  385 

compounds,  385 

hydroxide,  387 

oxide,  387 


INDEX. 


455 


Ferric  sulphate,  385 
Ferrous  chloride,  385 

compounds,  385 

hydroxide,  386 

oxide,  387 

sulphate,  357,  387 
Fertilizers,  332 
Fibrin,  403 
Fire-damp,  407 
Flame,  191 

reactions,  319 
Flames,  191,  192,  195 

luminosity  of,  198 
Flour,  428 
Fluorine,  235 
Fluor  spar,  235 
Formulas,  86,  212 
Formulas,  chemical,  86 
Franklinite,  342 
Freezing-point  method,  214 
Fusel-oil,  412 

Gadolinium,  20 
Gahnite,  342 
Galenite,  370 
Gall-nuts,  431 
Gallium,  226,  369 
Galvanized  iron,  343 
Gas,  illuminating-,  191 

marsh-,  406,  407 

olefiant-,  409 

water-,  42,  96,  191 
Gases,    combination   by   volume, 
150 

measurement  of,  56-61 

specific  gravity  of,  152,  205 

volumes  of  combining,  150,  211 
Gasoline,  406 
Gasometer,  25 
German  silver,  349,  389 
Germanium,  226,  370 
Glass,  275,  333 
Glucinum,  322 
Glucose,  410,  423 
Glucosides,  430,  432 
Glycerin,  412,  421 
Gold,  397,  399,  401 

alloys,  401 

chlorides,  402 

mining,  400 
Granite,  365 


Grape-sugar,  410 
Graphite,  169 
Guano,  417 
Gun-cotton,  427 
Gun-metal,  348 
Gunpowder,  306 
Gypsum,  329 

Haematite,  379,  387 

Hard  water,  188,  328,  330,  416 

Heat  of  combustion,  35 

decomposition,  37 
Helium,  20,  236 ' 
Heptanef406 
Hexane,  406 
Homologous  series,  407 
Homology,  406 
Hornblende,  339 
Hydrocarbons,  179,  403 
Hydrogen,  19,  39,  94,  132 

dioxide,  71,  98 

sulphide,  248 
Hydrosulphides,  247 
Hydroxides,  287 
Hydroxyl,  127 
Hypothesis  of  Avogadro,  205 

Iceland  spar,  327 
Illuminating-gas,  191 
Illumination,  191 
Incense,  431 

Indestructibility  of  matter,  74 
Indican,  432 
Indigo,  432 
Indium,  361 
Ink,  431 

sympathetic,  389 
Invert-sugar,  425 
Iodine,  232 
lodoforrn,  409 
lonization,  210 
Ions,  126,  187,  300 
Iridium,  397,  398 
Iron,  41,  93,  347,  379,  384 

alum,  387 

compounds,  385,  441 

galvanized,  343 

group,  379 

passive,  385 

pyrites,  388 

rust,  384 


456 


INDEX. 


Iron  sulphides,  388 
varieties  of,  381 

Kainite,  308 

Kaolin,  361,  365 

Kelp,  233 

Kerosene,  406 

Kieserite,  341 

Kindling-temperature,  33,  193 

Krypton,  20,  142 

Lamp-black,  171 
Lanthanum,  361 
Lapis  lazuli,  366 
"  Laughing-gas,"  162 
Law  of  Boyle,  57 

Dalton  and  Gay  Lussac,  56 

definite  proportions,  75 

Dulong  and  Petit,  360 

multiple  proportions,  77,  78 

specific  gravities  of  gases,  205 

heats  of  elements,  358 
Laws  of  Raoult,  214,  219 
Lead,  370 

acetate,  373,  414 

alloys,  371,  375 

black,  169 

carbonate,  373 

chloride,  373 

chromate,  373,  395 

oxide,  372 

peroxide,  372 

salts,  373,  438 

sulphate,  373 

sulphide,  374 

white,  374 

Leather,  preparation  of,  431 
Le  Blanc  process,  312 
Lepidolite,  319 
Levulose,  423,  424 
Light,   chemical   action   of,  108, 

357 

Lignite,  173 
Lime,  114,  145,  323 

light,  66 

Lime-water,  137,  138,  324 
Liquid  air,  141 
Litharge,  372 
Lithium,  319 
Litmus,  112,  121 
Luminosity  of  flames,  198 


"  Lunar  caustic,"  356 

Madder-root,  432 
Magenta,  430 
Magnesia,  114,  340 
Magnesite,  339 
Magnesium,  15,  339 

carbonate,  340 

chloride,  340 

compounds,  340,  444 

nitride,  340 

oxide,  114,  340 

sulphate,  340 
Magnetite,  379 
Manganese  chloride,  102 

compounds,  390,  442 

dioxide,  23,  93,  102,  390 

group,  390 

salts,  390 

sulphate,  103,  231 
Marble,  13,  322,  327 
Marl,  328,  366 
Marsh-gas,  406,  407 
Marsh's  test,  265 
Martin  steel,  383 
Matches,  260,  307 
Measurement  of  gases,  56-61 

heat,  36 

Mechanical  mixtures,  10 
Mendeleeff's  periodic  law,  222 

scheme,  224 
Meerschaum,  339 
Mercuric  chloride,  353 

oxide,  21,  88,  352 

sulphide,  353 
Mercurous  chloride,  352 
Mercury,  351 

compounds,  352,  438 
Metallic  properties,  129 
Metals,  96,  280 
Metathesis,  99 
Methane,  406 
Mica,  361,365 
Microcosmic  salt,  318 
Milk-sugar,  425 
Minium,  372 

Mixtures,  mechanical,  10 
Molasses,  425 
Molecular  formulas,  212 

weights,  determination  of,  205, 
2l4 


INDEX. 


457 


Molecules,  86,  205,  211 
of  the  elements,  208 
Molybdenum,  20 
Morphine,  433 
Mortar,  335 

Multiple  proportions,  law  of,  77, 
78 

Naphtha,  406 
Naphthalene,  404,  432 
Narcotine,  433 
Nascent  state,  210 
Natural  waters,  66 
Neodymium,  20 
Neon,  20,  142 
Neutralization,  121 
Nickel,  389 
Nicotine,  433 
Nitrates,  158,  293 
Nitric  oxide,  157, 163 
Nitrides,  144 
Nitrification,  144,  154 
Nitrobenzene,  429 
Nitrocellulose,  427 
Nitroglycerin,  420 
Nitrogen,  134,  258 

group,  258,  269 

oxides  of,  161 

pentoxide,  161 

peroxide,  158,  164 

trioxide,  161 
Nitrous  anhvdride,  1^0 

oxide,  161 
Nomenclature  of  acids,  129 

bases,  130 

chlorides,  107 

oxides,  107 

salts,  130 

Octane,  406 

Oil  of  bitter  almonds,  430 

illuminating,  406 

of  vitriol,  253 
Oleomargarin,  419 
Opium,  433 
Ores,  281 
Osmium,  397 
Oxidation,  64,  198 

slow,  34 
Oxides,  38,  286 

of  nitrogen,  161 


Oxides  of  nitrogen,  uses  of,  165, 
Oxygen,  18,  21,  25,  141 

and  the  sulphur  group,  256 
Oxyhydrogen  blowpipe,  65 
Ozone,  70,  209 

Paladium,  397 

Paper.  427 

Paraffin.  406 

Paraldehyde,  413 

Parkes's  'method,  354 

Passive  iron,  385 

Pattinson's  method,  354 

Peat,  173 

Pen  tan e,  406 

Periodic  law,  222 

Peruvian  bark,  433 

Petroleum,  405 

Phenol,  430 

Phosphates,  298 

Phosphine,  260 

Phosphonium  salts,  261 

Phosphorescence,  336 

Phosphorite,  258,  262,  331 

Phosphorus,  26,  28,  93,  133,  258 

acids  of,  262 

pentoxide,  94,  264 

red,  259 

Photography,  357 
Photometer,  192 
Physical  changes,  2 
Pinchbeck.  348 
Pitchblende,  396 
Plaster  of  Paris,  329 
Platinum,  397 

alloys,  398 

chloride,  319 
Polonium,  396 
Plumbago,  168 
Porcelain,  366,  367 
PotasE,  caustic,  40,  302 
Potassium,  39,  95,  112,  302 

acid  tartrate,  418 

chlorate,  22,  89,  115,  117,  307 

chloride,  92 

chlorplatinate,  318,  399 

chromate,  393 

compounds,  303,  445 

cyanide,  201,  202,  308 

dichromate,  393 

ferrocyanide,  201 


458 


INDEX. 


Potassium  fluosilicate,  319 

group,  802,  318 

hydroxide,  40,  304 

hypochlorite,  115,  117 

iodide,  304 

manganate,  390 

nitrate,  144,  305 

perchlorate,  92,  393 

permanganate,  45,  392 

sulphate,  308 
Praseodymium,  20 
Propane,  406 
Propylene,  407 
Puddling,  382 
' 'Purple  of  Cassius,"  402 
Pyrite,  388 
Pyroxylin,  427 

Quartation,  401 
Quartz,  274,  276 
Quartzite,  274,  276 
Quinine,  433 

Radicals,  421 
Radium,  396 
Raoult's  laws,  214,  219 
Reduction,  64,  178,  197 
Residues,  421 
Respiration,  179,  184 
Rhodium,  397 
Rock  crystal,  276 
Rubidium,  319 
Ruby,  363 

copper,  346 
Ruthenium,  397 

Safety-lamp,  194,  408 
Sal  ammoniac,  144,  316 
Salt,  common,  103,  109,  309,  312, 
313 

Epsom,  340 

Glauber's,  311 

microcosmic,  318 
Saltpetre,  144,  305 

Chili,  144,  154,  309 
Salts,  123,  125,  128,  255,  288 

acid,  255 

decomposition  of,  288 

ethereal,  418 

neutral,  255 

nomenclature  of,  130 


Salts,  normal,  255 
Samarium,  20 
Saponification,  419 
Sapphire,  363 
Scandium,  226,  369 
Selenium,  256 
Serpentine,  339 
Siderite,  379 
Silica,  274,  276 
Silicates,  298 
Silicic  acid,  275 

anhydride,  276 
Silicides,  275 
Silicon,  274 

dioxide,  276 

fluoride,  236,  275 

hydride,  275,  276 
Silver,  354 

alloys,  355 

compounds,  356,  358,  438 

chloride,  356,  358 

nitrate,  356 
Slow  oxidation,  34 
Smithsonite,  342 
Soaps,  415 
Soapstoue,  339 
Soda,  caustic,  40,  138,  310 

manufacture,  312,  313 
"  Soda-water,"  183 
Sodium,  39,  94,  308 

acid  carbonate,  314 

ammonium  phosphate,  318 

borate,  271,  315 

carbonate,  312 

chloride,  103,  109,  309,  311 

chlorplatinate,  399 

compounds,  309,  445 

hydroxide,  40,  138,  310 

"hyposulphite,"  311 

metaphosphate,  298 

nitrate,  144,  154,  311.— 

phosphate,  298,  314 

pyrophosphate,  298 

sulphate,  103,  112,  311,  312 

tetraborate.  272,  315 

thiosulphate,  311 
"Soft-soap,"  417 
Solder,  soft,  375 
Solution,  68,  69,  126,  300 
Solvay  process,  313 
Sorrels,  417 


INDEX. 


459 


Spathic  iron,  379 

Specific  beat  of  metals,  358 

Spectroscope,  320 

Spelter,  342 

Sphalerite,  342 

Spiegel-iron,  381 

Spinel,  364 

"  Spirits  of  hartshorn,"  146 

of  wine,  410 

Spiritu*  fumans  Libavii,  377 
Stannates,  376 
Stannic  acid,  376 

chloride,  377 

hydroxide,  376 

oxide,  376 

sulphide,  377 
Stannous  chloride,  376 

compounds,  375 
Starch,  403,  423,  427 
Stearin,  415 
Steel,  382 
Stibine,  267 
Strass,  334 
Strontium,  337 

Substituting  power  of  the   ele- 
ments, 216 
Substitution,  94,  408 
"  Sugar  of  lead,"  373,  414 
Sugar-refining,  425 
Sugars,  423 
Sulphates,  294 
Sulphides,  238,  243,  246,  291 
Sulphites,  296 
Sulphur,  27,  93,  218,  238 

dimorphism  of,  242 

dioxide,  248 
Sulphur  group,  238 

trioxide,  247,  250  \ 
Symbols,  18,  20 
Synthesis,  5! 

of  water,  53,  54,  55 

Tannin,  431 
Tanning,  431 
Tantalum,  269 
Tartar,  cream  of,  418 

emetic,  267 
Tellurium,  256,  399 
Thallium,  361 

Thomas-Gilchrist  process,  383 
Thorium,  277 


Thulium,  20 
Tin,  15,  157,  374 

alloys,  375 

amalgam,  375 

compounds,  375,  378,  438 
Titanium,  277 
Toluene,  404,  407,  429 
Tungsten,  20 
Turpentine,  105 

Ultramarine,  366 
Uranates,  396 
Uranium,  396 
Uranyl,  396 
compounds,  396 

Valence,  215 
Vanadium,  269 
Vapor-densities,  206 
Verdigris,  414 
Vitriol,  blue,  350 

green,  387 

oil  of,  253 

white,  344 

Water,  49,  67 
analysis  of,  51 
drinking,  67 
of  crystallization,  50 
hard,  188,  339,  341,  416 
in  neutralization,  125 
maximum  density  of,  68 
solvent  properties,  68 
synthesis  of,  53,  54,  55 
uses  of,  in  the  laboratory.  69 

"  Water-gas,"  42,  96,  189 

Waters,  natural,  66 

Water-vapor  in  the  air,  139,  140 

Weldon's  process,  391 

Wood-spirit,  404,  410 

Wood-vinegar,  414 

Wrought-iron,  382 

Xenon,  20,  142 
Xylene,  404,  407 

Yeast,  411 
Ytterbium,  361 
Yttrium,  361 

Zinc,  43,  44,  342 


460 


INDEX. 


Zinc  alloys,  343 
chloride,  44,  114,  344 
compounds,  345,  442 
dust,  342 
method,  854 


Zinc  oxide,  114,  344 
sulphate,  44,  844 
Zinc-white,  344 
Zircon,  277 
Zirconium,  277 


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1916 


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